© teacher created materials today’s lesson writing algebraic expressions

© Teacher Created Materials

Today’s Lesson

Writing Algebraic

Expressions


Let’s warm up today by finding patterns in numbers.

Warm-Up Activity


Find the missing numbers in the following patterns.

3, 6, 9, __ , 15, 18, __ , 24

1, 2, 4, __ , 11, 16, __ , 29

1, 1, 2, 3, 5, __ , 13, __


Check your answers.

3, 6, 9, 12, 15, 18, 21, 24

1, 2, 4, 7, 11, 16, 22, 29

1, 1, 2, 3, 5, 8, 13, 21


What is the pattern?

3, 6, 9, 12, 15, 18, 21, 24

+3 each time

+3 +3 +3 …



+1 more each time

+1 +2 +3 +4 …

1, 2, 4, 7, 11, 16, 22, 29



Add the 2 previousnumbers together

+0 +1 +1 +2 +3 +5 +8 1, 1, 2, 3, 5, 8, 13, 21


Today we will write algebraic expressions and find patterns in real-life situations to show

algebraically.

Whole-Class Skills Lesson


To review, what does the word variable mean?

A variable is an unknown quantity that has the potential to change.


What does the term algebraic expression mean?

An algebraic expression is any number sentence using variable(s) and number(s) in any combination.


How would you write the following expressions?

A number that is 5 more than 8

A number that is 5 more than t

A number that is 3 less than f

A number that is t less than f


How would you write the following expressions?

A number that is 5 more than 8

A number that is 5 more than t

A number that is 3 less than f

A number that is t less than f

8 + 5

t + 5

f – 3

f – t


Judy and her sister are born in the same month, but in different years. Judy is 5 years old and her sister is 2. When Judy turns 8, her sister will be 5. How old will Judy’s sister be when Judy is 14?


How did you solve that problem?

Just one of the ways to solve this problem is to make a T-chart.

This is a T-chart.

Judy’s age Sister’s age


Copy the T-chart below

Copy the data for Judy and her sister’s ages. This data comes

from the problem.


5 2

8 5

14


Do you see a pattern with Judy and her sister’s ages?


5 2

8 5

14

Judy’s sister’s age is always 3 years less than Judy’s age.


So based on the pattern, when Judy is 14, her sister will be three

years less than that—11 years old.


How old will Judy’s sister be when Judy is 20?

20 – 3 = 17

Judy’s sister will be 17.


How old will Judy’s sister be when Judy is 25?

25 – 3 = 22

Judy’s sister will be 22.


Assign a variable to Judy’s age.


5 2

8 5

14

Judy’s age can be represented by a variable, j

j

11


What is the best way to figure out Judy’s sister’s age using j as a

starting point?


We can write an algebraic for Judy’s sister’s age.

j – 3


Using j – 3, solve for Judy’s sister’s age when

j = 31

31 – 3 = 28

j = 45

45 – 3 = 42

© teacher created materials today’s lesson writing algebraic expressions

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