ncert solutions for class 11 maths chapter 1 sets aaash

NCERT solutions for class 11 maths chapter 1 Sets

Question:1(i) Which of the following are sets ?justify your answer

The collection of all the months of a year beginning with the letter J.

Answer:

The months starting with letter J are:

january

june

july

Hence,this is collection of well defined objects so it is a set.

Question:1(ii) Which of the following are sets ?justify your answer

The collection of ten most talented writers of India.

Answer:

Ten most talented writers may be different depending on different criteria of determining

talented writers.

Hence, this is not well defined so cannot be a set.

Question:1(iii) Which of the following are sets ?justify your answer

A team of eleven best-cricket batsmen of the world.

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Answer:

Eleven most talented cricketers may be different depending on criteria of determining

talent of a player.

Hence,this is not well defined so it is not a set.

Question:1(iv) Which of the following are sets ?justify your answer

The collection of all boys in your class.

Answer:

The collection of boys in a class are well defined and known.

Group of well defined objects is a set.

Hence, it is a set.

Question:1(v) Which of the following are sets? Justify your answer

The collection of all natural numbers less than 100.

Answer:

Natural numbers less than 100 has well defined and known collection of numbers.

that is S= {1,2,3............99}

Hence,it is a set.

Question:1(vi) Which of the following are sets? Justify your answer

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A collection of novels written by the writer Munshi Prem Chand.

Answer:

The collection of novels written by Munshi Prem Chand is well defined and known .

Hence,it is a set.

Question:1(vii) Which of the following are sets? Justify your answer

The collection of all even integers.

Answer:

The collection of even intergers is well defined because we can get even integers till

infinite. that is

Hence,it is a set.

Question:1(viii) Which of the following are sets? Justify your answer

The collection of questions in this Chapter.

Answer:

Collection of questions in a chapter is well defined and known .

Hence ,it is a set.

Question:1(ix) Which of the following are sets? Justify your answer

A collection of most dangerous animals of the world.

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Answer:

A Collection of most dangerous animal is not well defined because the criteria of

defining dangerousness of any animal can vary .

Hence,it is not a set.

Question:2

(i) 5_____A

(ii) 8_____A

(iii) 0_____A

(iv) 4_____A

(v) 2_____A

(vi) 10____A

Answer:

A = ,the elements which lie in this set belongs to this set and others do

not belong.

(i) 5 A

(ii) 8 A

(iii) 0 A

(iv) 4 A

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(v) 2 A

(vi) 10 A

Question:3(i) Write the following sets in roster form

Answer:

Elements of this set are:-3,-2,-1,0,1,2,3,4,5,6.

Hence ,this can be written as:

A =

Question:3(ii) Write the following sets in roster form

Answer:

Natural numbers less than 6 are: 1,2,3,4,5.

This can be written as:

Question:3(iii) Write the following sets in roster form

C = {x : x is a two-digit natural number such that the sum of its digits is 8}

Answer:

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The two digit numbers having sum equal to 8 are: 17,26,35,44,53,62,71,80.


Question:3(iv) Write the following sets in roster form

D = {x : x is a prime number which is divisor of 60}

Answer:

Prime numbers which are divisor of 60 are:2,3,5.


Question:3(v) Write the following sets in roster form

E = The set of all letters in the word TRIGONOMETRY.

Answer:

Letters of word TRIGONOMETRY are:T,R,I,G,N,O,M,E,Y.

This can be written as :

E = {T,R,I,G,N,O,M,E,Y}

Question:3(vi) Write the following sets in roster form

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F = The set of all letters in the word BETTER.

Answer:

The set of letters of word BETTER are: {B,E,T,R}


F = {B,E,T,R}

Question:4(i) Write the following sets in the set builder form

{3, 6, 9, 12}

Answer:

A = {3,6,9,12}

This can be written as :

Question:4(ii) Write the following sets in the set builder form

{2,4,8,16,32}

Answer:

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can be written as

Question:4(iii) Write the following sets in the set builder form:

{5, 25, 125, 625}

Answer:

can be written as

Question:4(iv) Write the following sets in the set builder form:

{2, 4, 6, . . .}

Answer:

This is a set of all even natural numbers.

{2,4,6....} can be written as {x : x is an even natural number}

Question:4(v) Write the following sets in the set builder form :

{1,4,9, . . .,100}

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Answer:

.

.

.

.

can be written as

Question:5(i) List all the elements of the following sets:

A = {x : x is an odd natural number}.

Answer:

A = { x : x is an odd natural number } = {1,3,5,7,9,11,13.............}

Question:5(ii) List all the elements of the following sets:

B= { x : x is an integer, }

Answer:

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Intergers between are 0,1,2,3,4.

Hence,B = {0,1,2,3,4}

Question:5(iii) List all the elements of the following sets:

C = {x : x is an integer, }

Answer:

Integers whose square is less than or equal to 4 are : -2,-1,0,1,2.

Hence,it can be written as c = {-2,-1,0,1,2}.

Question:5(iv) List all the elements of the following sets:

D = {x : x is a letter in the word “LOYAL”}

Answer:

LOYAL has letters L,O,Y,A.

D = {x : x is a letter in the word “LOYAL”} can be written as {L,O,Y,A}.

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Question:5(v) List all the elements of the following sets:

E = {x : x is a month of a year not having 31 days}

Answer:

The months not having 31 days are:

February

April

June

September

November

It can be written as {february,April,June,September,november}

Question:5(vi) List all the elements of the following sets :

F = {x : x is a consonant in the English alphabet which precedes k }.

Answer:

The consonents in english which precedes K are : B,C,D,F,G,H,J

Hence, F = {B,C,D,F,G,H,J}.

Question:6 Match each of the set on the left in the roster form with the same set on the

right described in set-builder form:

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(i) {1, 2, 3, 6} (a) {x : x is a prime number and a divisor of 6}

(ii) {2, 3} (b) {x : x is an odd natural number less than 10}

(iii) {M,A,T,H,E,I,C,S} (c) {x : x is natural number and divisor of 6}

(iv) {1, 3, 5, 7, 9} (d) {x : x is a letter of the word MATHEMATICS}.

Answer:

(i) 1,2,3,6 all are natural numbers and also divisors of 6.

Hence,(i) matches with (c)

(ii) 2,3 are prime numbers and are divisors of 6.

Hence,(ii) matches with (a).

(iii) M,A,T,H,E,I,C,S are letters of word "MATHEMATICS".

Hence, (iii) matches with (d).

(iv) 1,3,5,7,9 are odd natural numbers less than 10.

Hence,(iv) matches with (b).

NCERT solutions for class 11 maths chapter 1 sets-Exercise: 1.2

Question:1(i) Which of the following are examples of the null set :

Set of odd natural numbers divisible by 2

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Answer:

No odd number is divisible by 2.

Hence, this is a null set.

Question:1(ii) Which of the following are examples of the null set :

Set of even prime numbers.

Answer:

Even prime number = 2.

Hence, it is not a null set.

Question:1(iii) Which of the following are examples of the null set:

{ x : x is a natural numbers, and }

Answer:

No number exists which is less than 5 and more than 7.

Hence, this is a null set.

Question:1(iv) Which of the following are examples of the null set :

{ y : y is a point common to any two parallel lines}

Answer:

Parallel lines do not intersect so they do not have any common point.

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Hence, it is a null set.

Question:2 Which of the following sets are finite or infinite:

(i) The set of months of a year

(ii) {1, 2, 3, . . .}

(iii) {1, 2, 3, . . .99, 100}

(iv) ) The set of positive integers greater than 100.

(v) The set of prime numbers less than 99

Answer:

(i) Number of months in a year are 12 and finite.

Hence,this set is finite.

(ii) {1,2,3,4.......} and so on ,this does not have any limit.

Hence, this is infinite set.

(iii) {1,2,3,4,5......100} has finite numbers.

Hence ,this is finite set.

(iv) Positive integers greater than 100 has no limit.

Hence,it is infinite set.

(v) Prime numbers less than 99 are finite ,known numbers.

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Hence,it is finite set.

Question:3 State whether each of the following set is finite or infinite:

(i) The set of lines which are parallel to the x-axis

(ii) The set of letters in the English alphabet

(iii) The set of numbers which are multiple of 5

(iv) The set of animals living on the earth

(v) The set of circles passing through the origin (0,0)

Answer:

(i) Lines parallel to the x-axis are infinite.

Hence, it is an infinite set.

(ii) Letters in English alphabets are 26 letters which are finite.

Hence, it is a finite set.

(iii) Numbers which are multiple of 5 has no limit, they are infinite.


(iv) Animals living on earth are finite though the number is very high.

Hence, it is a finite set.

(v) There is an infinite number of circles which pass through the origin.

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Question:4(i) In the following, state whether A = B or not:

A = { a, b, c, d } B = { d, c, b, a }

Answer:

Given

A = {a,b,c,d}

B = {d,c,b,a}

Comparing the elements of set A and set B, we conclude that all the elements of A and

all the elements of B are equal.

Hence, A = B.

Question:4(ii) In the following, state whether A = B or not:

A = { 4, 8, 12, 16 } B = { 8, 4, 16, 18}

Answer:

12 belongs A but 12 does not belong to B

12 A but 12 B.

Hence, A B.

Question:4(iii) In the following, state whether A = B or not:

A = {2, 4, 6, 8, 10} B = { x : x is positive even integer and }

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Answer:

Positive even integers less than or equal to 10 are : 2,4,6,8,10.

So, B = { 2,4,6,8,10 } which is equal to A = {2,4,6,8,10}

Hence, A = B.

Question:4(iv) In the following, state whether A = B or not:

A = { x : x is a multiple of 10}, B = { 10, 15, 20, 25, 30, . . . }

Answer:

Multiples of 10 are : 10,20,30,40,........ till infinite.

SO, A = {10,20,30,40,.........}

B = {10,15,20,25,30........}

Comparing elements of A and B,we conclude that elements of A and B are not equal.

Hence, A B.

Question:5(i) Are the following pair of sets equal ? Give reasons.

A = {2, 3}, B = {x : x is solution of + 5x + 6 = 0}

Answer:

As given,

A = {2,3}

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And,

x = -2 and -3

B = {-2,-3}

Comparing elements of A and B,we conclude elements of A and B are not equal.

Hence,A B.

Question:5(ii) Are the following pair of sets equal ? Give reasons.

A = { x : x is a letter in the word FOLLOW}

B = { y : y is a letter in the word WOLF}

Answer:

Letters of word FOLLOW are F,OL,W.

SO, A = {F,O,L,W}

Letters of word WOLF are W,O,L,F.

So, B = {W,O,L,F}

Comparing A and B ,we conclude that elements of A are equal to elements of B.

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Hence, A=B.

Question:6 From the sets given below, select equal sets :

A = { 2, 4, 8, 12}, B = { 1, 2, 3, 4}, C = { 4, 8, 12, 14}, D = { 3, 1, 4, 2}

E = {–1, 1}, F = { 0, a}, G = {1, –1}, H = { 0, 1}

Answer:

Compare the elements of A,B,C,D,E,F,G,H.

8 A but

Now, 2 A but 2 C.

Hence, A B,A C,A D,A E,A F,A G,A H.

3 B,3 D but 3 C,3 E,3 F,3 G,3 H.

Hence,B C,B E,B F,B G,B H.

Similarly, comparing other elements of all sets, we conclude that elements of B and

elements of D are equal also elements of E and G are equal.

Hence, B=D and E = G.


Question:1 Make correct statements by filling in the symbols or in the blank

spaces :

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(i) { 2, 3, 4 } _____ { 1, 2, 3, 4,5 }

(ii) { a, b, c }______ { b, c, d }

(iii) {x : x is a student of Class XI of your school}______{x : x student of your school}

(iv) {x : x is a circle in the plane} ______{x : x is a circle in the same plane with radius 1

unit}

(v) {x : x is a triangle in a plane} ______ {x : x is a rectangle in the plane}

(vi) {x : x is an equilateral triangle in a plane} ______{x : x is a triangle in the same

plane}

(vii) {x : x is an even natural number} _____ {x : x is an integer}

Answer:

A set A is said to be a subset of a set B if every element of A is also an element of B.

(i). All elements {2,3,4} are also elements of {1,2,3,4,5} .

So, {2,3,4} {1,2,3,4,5}.

(ii).All elements { a, b, c } are not elements of{ b, c, d }.

Hence,{ a, b, c } { b, c, d }.

(iii) Students of class XI are also students of your school.

Hence,{x : x is a student of Class XI of your school} {x : x student of your school}

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(iv). Here, {x : x is a circle in the plane} {x : x is a circle in the same plane with radius

1 unit} : since a circle in the plane can have any radius

(v). Triangles and rectangles are two different shapes.

Hence,{x : x is a triangle in a plane} {x : x is a rectangle in the plane}

(vi). Equilateral triangles are part of all types of triangles.

So,{x : x is an equilateral triangle in a plane} {x : x is a triangle in the same plane}

(vii).Even natural numbers are part of all integers.

Hence, {x : x is an even natural number} {x : x is an integer}

Question:2 Examine whether the following statements are true or false:

(i) { a, b } { b, c, a }

(ii) { a, e } { x : x is a vowel in the English alphabet}

(iii) { 1, 2, 3 } { 1, 3, 5 }

(iv) { a } { a, b, c }

(v) { a } { a, b, c }

(vi) { x : x is an even natural number less than 6} { x : x is a natural number which

divides 36}

Answer:

(i) All elements of { a, b } lie in { b, c, a }.So,{ a, b } { b, c, a }.

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Hence,it is false.

(ii) All elements of { a, e } lie in {a,e,i,o,u}.

Hence,the statements given is true.

(iii) All elements of { 1, 2, 3 } are not present in { 1, 3, 5 }.

Hence,statement given is false.

(iv) Element of { a } lie in { a, b, c }.

Hence,the statement is true.

(v). { a } { a, b, c }

So,the statement is false.

(vi) All elements {2,4,} lies in {1,2,3,4,6,9,12,18,36}.


Question:3(i) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are incorrect

and why?

{3, 4} A

Answer:

3 {3,4} but 3 {1,2,{3,4},5}.

SO, {3, 4} A

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Hence,the statement is incorrect.

Question:3(ii) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are incorrect

and why?

{3, 4} A

Answer:

{3, 4} is element of A.

So, {3, 4} A.

Hence,the statement is correct.

Question:3(iii) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

{{3, 4}} A

Answer:

Here,

{ 3, 4 } { 1, 2, { 3, 4 }, 5 }

and { 3, 4 } {{3, 4}}

So, {{3, 4}} A.

Hence,the statement is correct.

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Question:3(iv) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

1 A

Answer:

Given, 1 is element of { 1, 2, { 3, 4 }, 5 }.

So,1 A.

Hence,statement is correct.

Question:3(v) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are incorrect

and why?

1 A

Answer:

Here, 1 is element of set A = { 1, 2, { 3, 4 }, 5 }.So,elements of set A cannot be subset of

set A.

1 { 1, 2, { 3, 4 }, 5 }.

Hence,the statement given is incorrect.

Question:3(vi) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

{1,2,5} A

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Answer:

All elements of {1,2,5} are present in { 1, 2, { 3, 4 }, 5 }.

So, {1,2,5} { 1, 2, { 3, 4 }, 5 }.

Hence,the statement given is correct.

Question:3(vii) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

{1,2,5} A

Answer:

Here,{1,2,5} is not an element of { 1, 2, { 3, 4 }, 5 }.

So,{1,2,5} A .

Hence, statement is incorrect.

Question:3(viii) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

{1,2,3} A

Answer:

Here, 3 {1,2,3}

but 3 { 1, 2, { 3, 4 }, 5 }.

So, {1,2,3} A

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Hence,the given statement is incorrect.

Question:3(ix) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

Answer:

is not an element of { 1, 2, { 3, 4 }, 5 }.

So, .

Hence,the above statement is incorrect.

Question:3(x) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are incorrect

and why?

Answer:

is subset of all sets.

Hence,the above statement is correct.

Question:3(xi) Let A = { 1, 2, { 3, 4 }, 5 }. Which of the following statements are

incorrect and why?

Answer:

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{ 1, 2, { 3, 4 }, 5 }. but is not an element of { 1, 2, { 3, 4 }, 5 }.

Hence, the above statement is incorrect.

Question:4(i) Write down all the subsets of the following sets

{a}

Answer:

Subsets of .

Question:4(ii) Write down all the subsets of the following sets:

{a, b}

Answer:

Subsets of . Thus the given set has 4 subsets

Question:4(iii) Write down all the subsets of the following sets:

{1,2,3}

Answer:

Subsets of

Question:4(iv) Write down all the subsets of the following sets:

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Answer:

Subset of is only.

The subset of a null set is null set itself

Question:5 How many elements has P(A), if A = ?

Answer:

Let the elements in set A be m, then n m

then, the number of elements in power set of A n

Here, A = so n 0

n 1

Hence,we conclude P(A) has 1 element.

Question:6 Write the following as intervals :

(i) {x : x R, – 4 x 6}

(ii) {x : x R, – 12 x –10}

(iii) {x : x R, 0 x 7}

(iv) {x : x R, 3 x 4}

Answer:

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The following can be written in interval as :

(i) {x : x R, – 4 x 6}

(ii) {x : x R, – 12 x –10}

(iii) {x : x R, 0 x 7}

(iv) (iv) {x : x R, 3 x 4}

Question:7 Write the following intervals in set-builder form :

(i) (– 3, 0)

(ii) [6 , 12]

(iii) (6, 12]

(iv) [–23, 5)

Answer:

The given intervals can be written in set builder form as :

(i) (– 3, 0)

(ii) [6 , 12]

(iii) (6, 12]

(iv) [–23, 5)

Question:8 What universal set(s) would you propose for each of the following :

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(i) The set of right triangles.

(ii) The set of isosceles triangles.

Answer:

(i) Universal set for a set of right angle triangles can be set of polygons or set of all

triangles.

(ii) Universal set for a set of isosceles angle triangles can be set of polygons.


Question:1(i) Find the union of each of the following pairs of sets :

X = {1, 3, 5} Y = {1, 2, 3}

Answer:

Union of X and Y is X Y = {1,2,3,5}

Question:1(ii) Find the union of each of the following pairs of sets :

A = [ a, e, i, o, u} B = {a, b, c}

Answer:

Union of A and B is A B = {a,b,c,e,i,o,u}.

Question:1(iii) Find the union of each of the following pairs of sets :

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A = {x : x is a natural number and multiple of 3} B = {x : x is a natural number less than

6}

Answer:

Here ,

A = {3,6,9,12,15,18,............}

B = {1,2,3,4,5,6}

Union of A and B is A B.

A B = {1,2,3,4,5,6,9,12,15........}

Question:1(iv) Find the union of each of the following pairs of sets :

A = {x : x is a natural number and 1 x 6 }

B = {x : x is a natural number and 6 x 10 }

Answer:

Here,

A = {2,3,4,5,6}

B = {7,8,9}

A B = {2,3,4,5,6,7,8,9}

or it can be written as A B = {x : x is a natural number and 1 x 10 }

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Question:1(v) Find the union of each of the following pairs of sets :

A = {1, 2, 3} B =

Answer:

Here,

A union B is A B.

A B = {1,2,3}

Question:2 Let A = { a, b }, B = {a, b, c}. Is A B ? What is A B ?

Answer:

Here,

We can see elements of A lie in set B.

Hence, A B.

And, A B = {a,b,c} = B

Question:3 If A and B are two sets such that A B, then what is A B ?

Answer:

If A is subset of B then A B will be set B.

Question:4(i) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

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A B

Answer:

Here,

A = {1, 2, 3, 4}

B = {3, 4, 5, 6}

The union of the set can be written as follows

A B = {1,2,3,4,5,6}

Question:4(ii) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

A C

Answer:

Here,

A = {1, 2, 3, 4}

C = {5, 6, 7, 8 }

The union can be written as follows

A C = {1,2,3,4,5,6,7,8}

Question:4(iii) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

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B C

Answer:

Here,

B = {3, 4, 5, 6},

C = {5, 6, 7, 8 }

The union of the given sets are

B C = { 3,4,5,6,7,8}

Question:4(iv) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

B D

Answer:

Here,

B = {3, 4, 5, 6}

D = { 7, 8, 9, 10 }

B D = {3,4,5,6,7,8,9,10}

Question: 4(v) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

A B C

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Answer:

Here,

A = {1, 2, 3, 4},

B = {3, 4, 5, 6},

C = {5, 6, 7, 8 }

The union can be written as

A B C = {1,2,3,4,5,6,7,8}

Question:4(vi) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

A B D

Answer:

Here,

A = {1, 2, 3, 4},

B = {3, 4, 5, 6}

D = { 7, 8, 9, 10 }


A B D = {1,2,3,4,5,6,7,8,9,10}

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Question:4(vii) If A = {1, 2, 3, 4}, B = {3, 4, 5, 6}, C = {5, 6, 7, 8 }and D = { 7, 8, 9, 10 };

find

B C D

Answer:

Here,B = {3, 4, 5, 6},

C = {5, 6, 7, 8 } and

D = { 7, 8, 9, 10 }


B C D = {3,4,5,6,7,8,9,10}

Question:5 Find the intersection of each pair of sets of question 1 above

(i) X = {1, 3, 5} Y = {1, 2, 3}

(ii) A = [ a, e, i, o, u} B = {a, b, c}

(iii) A = {x : x is a natural number and multiple of 3} B = {x : x is a natural number less

than 6}

(iv) A = {x : x is a natural number and 1 x 6 } B = {x : x is a natural number and

6 x 10 }

(v) A = {1, 2, 3}, B =

Answer:

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(i) X = {1, 3, 5} Y = {1, 2, 3}

X Y = {1,3}

(ii) A = [ a, e, i, o, u} B = {a, b, c}

A B = {a}

(iii) A = {x : x is a natural number and multiple of 3} B = {x : x is a natural number less

than 6}

A = {3,6,9,12,15.......} B = {1,2,3,4,5}

A B = {3}

(iv)A = {x : x is a natural number and 1 x 6 } B = {x : x is a natural number and

6 x 10 }

A = {2,3,4,5,6} B = {7,8,9}

A B =

(v) A = {1, 2, 3}, B =

A B =

Question:6 If A = { 3, 5, 7, 9, 11 }, B = {7, 9, 11, 13}, C = {11, 13, 15}and D = {15, 17};

find

(i) A B (ii) B C

(iii) A C D (iv) A C

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(v) B D (vi) A (B C)

(vii) A D (viii) A (B D)

(ix) ( A B ) ( B C ) (x) ( A D) ( B C)

Answer:

Here, A = { 3, 5, 7, 9, 11 }, B = {7, 9, 11, 13}, C = {11, 13, 15} and D = {15, 17}

(i) A B = {7,9,11} (vi) A (B C) = {7,9,11}

(ii) B C = { 11,13} (vii) A D =

(iii) A C D = (viii) A (B D) = {7,9,11}

(iv) A C = { 11 } (ix) ( A B ) ( B C ) = {7,9,11}

(v) B D = (x) ( A D) ( B C) = {7,9,11,15}

Question:7 If A = {x : x is a natural number }, B = {x : x is an even natural number} C =

{x : x is an odd natural number} and D = {x : x is a prime number }, find

(i) A B

(ii) A C

(iii) A D

(iv) B C

(v) B D

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(vi) C D

Answer:

Here, A = {1,2,3,4,5,6...........}

B = {2,4,6,8,10...........}

C = {1,3,5,7,9,11,...........}

D = {2,3,5,7,11,13,17,......}

(i) A B = {2,4,6,8,10........} = B

(ii) A C = {1,3,5,7,9.........} = C

(iii) A D = {2,3,5,7,11,13.............} = D

(iv) B C =

(v) B D = {2}

(vi) C D = {3,5,7,11,13,..........} =

Question:8(i) Which of the following pairs of sets are disjoint

{1, 2, 3, 4} and {x : x is a natural number and 4 x 6 }

Answer:

Here, {1, 2, 3, 4} and {4,5,6}

{1, 2, 3, 4} {4,5,6} = {4}

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Hence,it is not a disjoint set.

Question:8(ii) Which of the following pairs of sets are disjoint

{ a, e, i, o, u } and { c, d, e, f }

Answer:

Here, { a, e, i, o, u } and { c, d, e, f }

{ a, e, i, o, u } { c, d, e, f } = {e}

Hence,it is not disjoint set.

Question:8(iii) Which of the following pairs of sets are disjoint

{x : x is an even integer } and {x : x is an odd integer}

Answer:

Here, {x : x is an even integer } and {x : x is an odd integer}

{2,4,6,8,10,..........} and {1,3,5,7,9,11,.....}

{2,4,6,8,10,..........} {1,3,5,7,9,11,.....} =

Hence,it is disjoint set.

Question:9 If A = {3, 6, 9, 12, 15, 18, 21}, B = { 4, 8, 12, 16, 20 }, C = { 2, 4, 6, 8, 10,

12, 14, 16 }, D = {5, 10, 15, 20 }; find

(i) A – B (ii) A – C (iii) A – D (iv) B – A (v) C – A (vi) D – A

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(vii) B – C (viii) B – D (ix) C – B (x) D – B (xi) C – D (xii) D – C

Answer:

A = {3, 6, 9, 12, 15, 18, 21}, B = { 4, 8, 12, 16, 20 }, C = { 2, 4, 6, 8, 10, 12, 14, 16 }, D =

{5, 10, 15, 20 }

The given operations are done as follows

(i) A – B = {3,6,9,15,18,21} (vii) B – C = {20}

(ii) A – C = {3,9,15,18,21} (viii) B – D = {4,8,12,16}

(iii) A – D = {3,6,9,12,18,21} (ix) C – B = {2,6,10,14}

(iv) B – A = {4,8,16,20} (x) D – B = {5,10,15}

(v) C – A = {2,4,8,10,14,16} (xi) C – D = {2,4,6,8,12,14,16}

(vi) D – A = {5,10,20} (xii) D – C = {5,15,20}

Question:10 If X= { a, b, c, d } and Y = { f, b, d, g}, find

(i) X – Y

(ii) Y – X

(iii) X Y

Answer:

X= { a, b, c, d } and Y = { f, b, d, g}

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(i) X – Y = {a,c}

(ii) Y – X = {f,g}

(iii) X Y = {b,d}

Question:11 If R is the set of real numbers and Q is the set of rational numbers, then

what is R – Q ?

Answer:

R = set of real numbers.

Q = set of rational numbers.

R - Q = set of irrational numbers.

Question:12(i) State whether each of the following statement is true or false. Justify

your answer.

{ 2, 3, 4, 5 } and { 3, 6} are disjoint sets.

Answer:

Here,

{ 2, 3, 4, 5 } and { 3, 6}

{ 2, 3, 4, 5 } { 3, 6} = {3}

Hence,these are not disjoint sets.

So,false.

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Question:12(ii) State whether each of the following statement is true or false. Justify

your answer.

{ a, e, i, o, u } and { a, b, c, d }are disjoint sets

Answer:

Here, { a, e, i, o, u } and { a, b, c, d }

{ a, e, i, o, u } { a, b, c, d } = {a}

Hence,these are not disjoint sets.

So, statement is false.

Question:12(iii) State whether each of the following statement is true or false. Justify

your answer.

{ 2, 6, 10, 14 } and { 3, 7, 11, 15} are disjoint sets.

Answer:

Here,

{ 2, 6, 10, 14 } and { 3, 7, 11, 15}

{ 2, 6, 10, 14 } { 3, 7, 11, 15} =

Hence, these are disjoint sets.

So,given statement is true.

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Question:12(iv) State whether each of the following statement is true or false. Justify

your answer.

{ 2, 6, 10 } and { 3, 7, 11} are disjoint sets.

Answer:

Here,

{ 2, 6, 10 } and { 3, 7, 11}

{ 2, 6, 10 } { 3, 7, 11} =

Hence,these are disjoint sets.

So,statement is true.

NCERT solutions for maths class 11 chapter 1 sets-Exercise: 1.5

Question:1 Let U = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }, A = { 1, 2, 3, 4}, B = { 2, 4, 6, 8 } and C = {

3, 4, 5, 6 }. Find

(i) A′

(ii) B′

(iii) (A C)′

(iv) (A B)′

(v) (A')'

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(vi) (B – C)'

Answer:

U = { 1, 2, 3, 4, 5, 6, 7, 8, 9 }, A = { 1, 2, 3, 4}, B = { 2, 4, 6, 8 } and C = { 3, 4, 5, 6 }

(i) A′ = U - A = {5,6,7,8,9}

(ii) B′ = U - B = {1,3,5,7,9}

(iii) A C = {1,2,3,4,5,6}

(A C)′ = U - (A C) = {7,8,9}

(iv) (A B) = {1,2,3,4,6,8}

(A B)′ = U - (A B) = {5,7,9}

(v) (A')' = A = { 1, 2, 3, 4}

(vi) (B – C) = {2,8}

(B – C)' = U - (B – C) = {1,3,4,5,6,7,9}

Question:2 If U = { a, b, c, d, e, f, g, h}, find the complements of the following sets :

(i) A = {a, b, c}

(ii) B = {d, e, f, g}

(iii) C = {a, c, e, g}

(iv) D = { f, g, h, a}

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Answer:

U = { a, b, c, d, e, f, g, h}

(i) A = {a, b, c}

A' = U - A = {d,e,f,g,h}

(ii) B = {d, e, f, g}

B' = U - B = {a,b,c,h}

(iii) C = {a, c, e, g}

C' = U - C = {b,d,f,h}

(iv) D = { f, g, h, a}

D' = U - D = {b,c,d,e}

Question:3 Taking the set of natural numbers as the universal set, write down the

complements of the following sets:

(i) {x : x is an even natural number}

(ii) { x : x is an odd natural number }

(iii) {x : x is a positive multiple of 3}

(iv) { x : x is a prime number }

(v) {x : x is a natural number divisible by 3 and 5}

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Answer:

Universal set = U = {1,2,3,4,5,6,7....................}

(i) {x : x is an even natural number} = {2,4,6,8,..........}

{x : x is an even natural number}'= U - {x : x is an even natural number} =

{1,3,5,7,9,..........} = {x : x is an odd natural number}

(ii) { x : x is an odd natural number }' = U - { x : x is an odd natural number } = {x : x is an

even natural number}

(iii) {x : x is a positive multiple of 3}' = U - {x : x is a positive multiple of 3} = {x : x , x N

and is not a positive multiple of 3}

(iv) { x : x is a prime number }' = U - { x : x is a prime number } = { x : x is a positive

composite number and 1 }

(v) {x : x is a natural number divisible by 3 and 5}' = U - {x : x is a natural number

divisible by 3 and 5} = {x : x is a natural number not divisible by 3 or 5}

Question:3 Taking the set of natural numbers as the universal set, write down the

complements of the following sets:

(vi) { x : x is a perfect square }

(vii) { x : x is a perfect cube}

(viii) { x : x + 5 8 }

(ix) { x : 2x + 5 9}

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(x) { x : x 7 }

(xi) { x : x N and 2x + 1 10 }

Answer:

Universal set = U = {1,2,3,4,5,6,7,8.............}

(vi) { x : x is a perfect square }' = U - { x : x is a perfect square } = { x : x N and x is not

a perfect square }

(vii) { x : x is a perfect cube}' = U - { x : x is a perfect cube} = { x : x N and x is not a

perfect cube}

(viii) { x : x + 5 8 }' = U - { x : x + 5 8 } = U - {3} = { x : x N and x 3 }

(ix) { x : 2x + 5 9}' = U - { x : 2x + 5 9} = U -{2} = { x : x N and x 2}

(x) { x : x 7 }' = U - { x : x 7 } = { x : x N and x 7 }

(xi) { x : x N and 2x + 1 10 }' = U - { x : x N and x 9/2 } = { x : x N and x 9/2 }

Question:4 If U = {1, 2, 3, 4, 5, 6, 7, 8, 9 }, A = {2, 4, 6, 8} and B = { 2, 3, 5, 7}. Verify

that

(i) (A B)′ = A′ B′

(ii) (A B)′ = A′ B′

Answer:

U = {1, 2, 3, 4, 5, 6, 7, 8, 9 }, A = {2, 4, 6, 8} and B = { 2, 3, 5, 7}

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(i) (A B)′ = A′ B′

L.H.S = (A B)′ = U - (A B) = {1,9}

R.H.S = A′ B′ = {1,3,5,7,9} {1,4,6,8,9} = {1,9}

L.H.S = R.H.S


(ii) (A B)′ = A′ B′

L.H.S = U - (A B) ={1,3,4,5,6,7,8,9}

R.H.S = A′ B′ = {1,3,5,7,9} {1,4,6,8,9} = {1,3,4,5,6,7,8,9}

L.H.S = R.H.S


Question:5 Draw appropriate Venn diagram for each of the following :

(i) (A ∪ B)′

(ii) A′ ∩ B′

(iii) (A ∩ B)′

(iv) A′ ∪ B′

Answer:

(i) (A ∪ B)′

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(A ∪ B) is in yellow colour

(A ∪ B)′ is in green colour

ii) A′ ∩ B′ is represented by the green colour in the below figure

iii) (A ∩ B)′ is represented by green colour in the below diagram and white colour

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iv) A′ ∪ B′

The green colour represents A′ ∪ B′

Question:6 Let U be the set of all triangles in a plane. If A is the set of all triangles with

at least one angle different from , what is A′?

Answer:

A' is the set of all triangles whose angle is in other words A' is set of all equilateral

triangles.

Question:7 Fill in the blanks to make each of the following a true statement :

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(i) A A′

(ii) A

(iii) A A′

(iv) U′ A

Answer:

The following are the answers for the questions

(i) A A′ U

(ii) ′ A A

(iii) A A′

(iv) U′ A


Question:1 If X and Y are two sets such that n ( X ) = 17, n ( Y ) = 23 and n ( X Y ) =

38, find n ( X Y ).

Answer:

n( X ) = 17, n( Y ) = 23 and n( X Y ) = 38

n( X Y ) = n( X ) + n( Y ) - n ( X Y )

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38 = 17 + 23 - n ( X Y )

n ( X Y ) = 40 - 38

n ( X Y ) = 2.

Question:2 If X and Y are two sets such that X Y has 18 elements, X has 8 elements

and Y has 15 elements ; how many elements does X Y have?

Answer:

n( X Y ) = 18

n(X) = 8

n(Y) = 15

n( X Y ) = n(X) + n(Y) - n(X Y)

n(X Y) = 8 + 15 - 18

n(X Y) = 5

Question:3 In a group of 400 people, 250 can speak Hindi and 200 can speak English.

How many people can speak both Hindi and English?

Answer:

Hindi speaking = 250 = n(A)

English speakind = 200 = n(B)

Group of people = 400 = n(A B)

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People speaking both Hindi and English = n(A B)

n(A B) = n(A) + n(B) - n(A B)

n(A B) = 250 + 200 - 400

n(A B) = 450 - 400

n(A B) = 50

Thus,50 people speak hindi and english both.

Question:4 If S and T are two sets such that S has 21 elements, T has 32 elements,

and S T has 11 elements, how many elements does S T have?

Answer:

n(S) = 21

n(T) = 32

n(S T) = 11

n(S T) = n(S) + n(T) - n(S T)

n(S T) = 21 + 32 - 11

n(S T) = 53 - 11

n(S T) = 42

Hence, the set (S T) has 42 elements.

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Question:5 If X and Y are two sets such that X has 40 elements, X Y has 60

elements and X Y has 10 elements, how many elements does Y have?

Answer:

n( X Y) = 60

n( X ∩ Y) = 10

n(X) = 40

n( X Y) = n(X) + n(Y) - n( X ∩ Y)

n(Y) = 60 - 40 + 10

n(Y) = 30

Hence,set Y has 30 elements.

Question:6 In a group of 70 people, 37 like coffee, 52 like tea and each person likes at

least one of the two drinks. How many people like both coffee and tea?

Answer:

n(people like coffee) = 37

n(people like tea ) = 52

Total number of people = 70

Total number of people = n(people like coffee) + n(people like tea ) - n(people like both

tea and coffee)

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70 = 37 + 52 - n(people like both tea and coffee)

n(people like both tea and coffee) = 89 - 70

n(people like both tea and coffee) = 19

Hence,19 people like both coffee and tea.

Question:7 In a group of 65 people, 40 like cricket, 10 like both cricket and tennis. How

many like tennis only and not cricket? How many like tennis?

Answer:

Total people = 65

n(like cricket) = 40

n(like both cricket and tennis) = 10

n(like tennis) = ?

Total people = n(like cricket) + n(like tennis) - n(like both cricket and tennis)

n(like tennis) = 65 - 40 + 10

n(like tennis) = 35

Hence,35 people like tennis.

n (people like only tennis) = n(like tennis) - n(like both cricket and tennis)

n (people like only tennis) = 35 - 10

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n (people like only tennis) = 25

Hence,25 people like only tennis.

Question:8 In a committee, 50 people speak French, 20 speak Spanish and 10 speak

both Spanish and French. How many speak at least one of these two languages?

Answer:

n(french) = 50

n(spanish) = 20

n(speak both french and spanish) = 10

n(speak at least one of these two languages) = n(french) + n(spanish) - n(speak both

french and spanish)

n(speak at least one of these two languages) = 50 + 20 - 10

n(speak at least one of these two languages) = 70 -10

n(speak at least one of these two languages) = 60

Hence,60 people speak at least one of these two languages.

NCERT solutions for class 11 maths chapter 1 sets-Miscellaneous Exercise Aak

ash I

nstitu

te

Question:1 Decide, among the following sets, which sets are subsets of one and

another:

A = { x : x R and x satisfy – 8x + 12 = 0 }, B = { 2, 4, 6 },

C = { 2, 4, 6, 8, . . . }, D = { 6 }.

Answer:

Solution of this equation are – 8x + 12 = 0

( x - 2 ) ( x - 6 ) = 0

X = 2,6

A = { 2,6 }

B = { 2, 4, 6 }

C = { 2, 4, 6, 8, . . . }

D = { 6 }

From the sets given above, we can conclude that A B, A C, D A, D B, D C,

B C

Hence, we can say that D A B C

Question:2(i) In each of the following, determine whether the statement is true or false.

If it is true, prove it. If it is false, give an example.

If x A and A B , then x B

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Answer:

The given statment is false,

example: Let A = { 2,4 }

B = { 1,{2,4},5}

x be 2.

then, 2 { 2,4 } = x A and { 2,4 } { 1,{2,4},5} = A B

But 2 { 1,{2,4},5} i.e. x B

Question:2(ii) In each of the following, determine whether the statement is true or false.


If A B and B C , then A C

Answer:

The given statement is false,

Let , A = {1}

B = { 1,2,3}

C = {0,{1,2,3},4}

Here, {1} { 1,2,3} = A B and { 1,2,3} {0,{1,2,3},4} = B C

But, {1} {0,{1,2,3},4} = A C

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Question:2(iii) In each of the following, determine whether the statement is true or

false. If it is true, prove it. If it is false, give an example.


Answer:

Let A ⊂ B and B ⊂ C

There be a element x such that

Let, x A

x B ( Because A B )

x C ( Because B C )

Hence,the statement is true that A C

Question:2(iv) In each of the following, determine whether the statement is true or



Answer:

The given statement is false

Let , A = {1,2}

B = {3,4,5 }

C = { 1,2,6,7,8}

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Here, {1,2} {3,4,5 } = A B and {3,4,5 } { 1,2,6,7,8} = B C

But , {1,2} { 1,2,6,7,8} = A C

Question:2(v) In each of the following, determine whether the statement is true or false.


If x A and A B , then x B

Answer:

The given statement is false,

Let x be 2

A = { 1,2,3}

B = { 4,5,6,7}

Here, 2 { 1,2,3} = x A and { 1,2,3} { 4,5,6,7} = A B

But, 2 { 4,5,6,7} implies x B

Question:2(vi) In each of the following, determine whether the statement is true or


If A B and x B , then x A

Answer:

The given statement is true,

Let, A B and x B

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Suppose, x A

Then, x B , which is contradiction to x B

Hence, x A.

Question:3 Let A, B, and C be the sets such that A B = A C and A B = A C.

Show that B = C.

Answer:

Let A, B, and C be the sets such that A B = A C and A B = A C

To prove : B = C.

A B = A + B - A B = A C = A + C - A C

A + B - A B = A + C - A C

B - A B = C - A C ( since A B = A C )

B = C

Hence proved that B= C.

Question:4 Show that the following four conditions are equivalent :

(i) A B(ii) A – B = (iii) A B = B (iv) A B = A

Answer:

First, we need to show A B A – B =

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Let A B

To prove : A – B =

Suppose A – B

this means, x A and x B , which is not possible as A B .

SO, A – B = .

Hence, A B A – B = .

Now, let A – B =

To prove : A B

Suppose, x A

A – B = so x B

Since, x A and x B and A – B = so A B

Hence, A B A – B = .

Let A B

To prove : A B = B

We can say B A B

Suppose, x A B

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means x A or x B

If x A

since A B so x B

Hence, A B = B

and If x B then also A B = B.

Now, let A B = B

To prove : A B

Suppose : x A

A A B so x A B

A B = B so x B

Hence,A B

ALSO, A B A B = B

NOW, we need to show A B A B = A

Let A B

To prove : A B = A

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Suppose : x A

We know A B A

x A B Also ,A A B

Hence, A B = A

Let A B = A

To prove : A B

Suppose : x A

x A B ( replacing A by A B )

x A and x B

A B

A B A B = A

Question:5 Show that if A B, then C – B C – A.

Answer:

Given , A B

To prove : C – B C – A

Let, x C - B means x C but x B

A B so x C but x A i.e. x C - A

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Hence, C – B C – A

Question:6 Assume that P ( A ) = P ( B ). Show that A = B

Answer:

Given, P ( A ) = P ( B )

To prove : A = B

Let, x A

A P ( A ) = P ( B )

For some C P ( B ) , x C

Here, C B

Therefore, x B and A B

Similarly we can say B A.

Hence, A = B

Question:7 Is it true that for any sets A and B, P ( A ) ∪ P ( B ) = P ( A ∪ B )? Justify

your answer.

Answer:

No, it is false.

To prove : P ( A ) ∪ P ( B ) P ( A ∪ B )

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Let, A = {1,3} and B = {3,4}

A B = {1,3,4}

P(A) = { { },{1},{3},{1,3}}

P(B) = { { },{3},{4},{3,4}}

L.H.S = P(A) P(B) = { { },{1},{3},{1,3},{3,4},{4}}

R.H.S.= P(A B) = { { },{1},{3},{1,3},{3,4},{4},{1,4},{1,3,4}}

Hence, L.H.S. R.H.S

Question:8 Show that for any sets A and B,

A = ( A B ) ( A – B ) and A ( B – A ) = ( A B )

Answer:

A = ( A B ) ( A – B )

L.H.S = A = Red coloured area

R.H.S = ( A B ) ( A – B )

( A B ) = green coloured

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( A – B ) = yellow coloured

( A B ) ( A – B ) = coloured part

Hence, L.H.S = R.H.S = Coloured part

A ( B – A ) = ( A B )

A = sky blue coloured

( B – A )=pink coloured

L.H.S = A ( B – A ) = sky blue coloured + pink coloured

R.H.S = ( A B ) = brown coloured part

L.H.S = R.H.S = Coloured part

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Question:9(i) Using properties of sets, show that

A ( A B ) = A

Answer:

(i) A ( A B ) = A

We know that A A

and A B A

A ( A B ) A

and also , A A ( A B )

Hence, A ( A B ) = A

Question:9(ii) Using properties of sets, show that

A ( A B ) = A

Answer:

This can be solved as follows

(ii) A ( A B ) = A

A ( A B ) = (A A) ( A B )

A ( A B ) = A ( A B ) { A ( A B ) = A proved in 9(i)}

A ( A B ) = A

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Question:10 Show that A B = A C need not imply B = C.

Answer:

Let, A = {0,1,2}

B = {1,2,3}

C = {1,2,3,4,5}

Given, A B = A C

L.H.S : A B = {1,2}

R.H.S : A C = {1,2}

and here {1,2,3} {1,2,3,4,5} = B C.

Hence, A B = A C need not imply B = C.

Question:11 Let A and B be sets. If A X B X and A X B X for some

set X, show that A B.

Answer:

Given, A X B X and A X B X

To prove: A = B

A = A (A X) (A X B X)

= A (B X)

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= (A B) (A X)

= (A B) (A X )

= (A B)

B = B (B X) (A X B X)

= B (A X)

= (B A) (B X)

= (B A) (B X )

= (B A)

We know that (A B) = (B A) = A = B

Hence, A = B

Question:12 Find sets A, B and C such that A B, B C and A C are non-empty

sets and A B C

Answer:

Given, A B, B C and A C are non-empty sets

To prove : A B C

Let A = {1,2}

B = {1,3}

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C = {3,2}

Here, A B = {1}

B C = {3}

A C = {2}

and A B C

Question:13 In a survey of 600 students in a school, 150 students were found to be

taking tea and 225 taking coffee, 100 were taking both tea and coffee. Find how many

students were taking neither tea nor coffee?

Answer:

n ( taking tea) = 150

n (taking coffee) = 225

n ( taking both ) = 100

n(people taking tea or coffee) = n ( taking tea) + n (taking coffee) - n ( taking both )

= 150 + 225 - 100

=375 - 100

= 275

Total students = 600

n(students taking neither tea nor coffee ) = 600 - 275 = 325

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Hence,325 students were taking neither tea nor coffee.

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ncert solutions for class 11 maths chapter 1 sets aaash

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