dec. 3, 2013
TRANSCRIPT
Today:
Warm-Up:
These fractions represent the only three ways to convert fractions to decimals. The denominator: a.) Is one of the place valuesb.) Divides evenly into one of the place values: Multiply top and bottom by that amountc.) Either does not divide evenly into a place value, or you are not sure: Divide the numerator by the denominator
.21 .44 .55
.6 .28.18 .44 .375
What % of 10 is 1?
1 ÷ 10 = .10
What % of 20 is
2?2 ÷ 20 = .10 = 10%
Warm-Up:
= 10%
Warm Up
A. 10% of $1.00 is .1, or (.10 cents). To find 10%, simply move the decimal one place to the left.
Mental Math: Percent of a Number
Find 10% using mental
math
To find 20% of any number, multiply by 2 and move
the decimal one place to the left.
Find 20% using mental math1)
20
3)
42.1
1) 10
3) 60
4) 380
Find 5% using mental math 4)
160
1)
10
3)
60 4) 125
B. 20% is what
fraction?
.2
2) 25
2) 20
2) 3.5
20% of 40
is…..
8
Vocabulary:
14
21,
2
3
17
16,
9
8
2
6
3
5
x3
7
14
6
x
Solve each proportion.
Use Cross Multiplication to determine if each pairs of ratios form a proportion.
Practice:
Solving Percent Problems
Percent IS
100 OF
=
% = is unknown
100 of25 = x 100 60
Cross multiply to find: 100x = 30(80)
30% of 80 is what number?
When solving for the part, it’s often easier to multiply the whole by the decimal form of the percent:
80x .3
24
% = is
100 of20 = 30 100 x
Cross multiply to find: 20x = 30(100)
20x = 3000 (divide both sides by 20)
x = 150
20% of what number is 30?
x = 6, so our answer is 6%
What percent of 200 is 12?% = is 100 of
x = 12 100 200
200x = 12(100)
200x = 1200
% = is 100 of
x = 36 100 150
1. What is 45% of 120? What are we solving for?
45 = x 100 120
First try using mental math to solve
Then set up a proportion
3. 48 is 300% of what number?
2. 36 is what percent of 30? x = 36
100 30