1. Today:

2. Warm-Up:
.21
.44
.55
These fractions represent the only three ways to convert fractions
to decimals. The denominator: a.) Is one of the place values
b.) Divides evenly into one of the place values: Multiply top
and bottom by that amount
c.) Either does not divide evenly into a place value, or you
are not sure: Divide the numerator by the denominator
.6
.18
.44
.28
.375

3. Warm-Up:
What % of 10 is 1?
1 ÷ 10 = .10
= 10%
What % of 20 is
2 ÷ 20 = 2? = 10%
.10

4. Warm Up
Mental Math: Percent of a Number
A. 10% of $1.00 is .1, or (.10 cents). To find 10%, simply
move the decimal one place to the left.
B. 20% is what
fraction?
.2
To find 20% of any number, multiply by 2 and move
8
the decimal one place to the left. 40
20% of
is…..
4) 380
1) 10 2) 25 3)
Find 10% using mental
42.1
math
2) 20 3)
1)
4)
Find 5% using mental math
10 2) 3.5 3) 60 4) 125
60
160
Find 20% using mental math
1)
20

5. Vocabulary:

6. Practice:
Use Cross Multiplication to determine if each pairs of
ratios form a proportion.
3 21
,
2 14
8 16
,
9 17
Solve each proportion.
6
14
7
x 3
5
3
6
x 2

8. Solving Percent Problems

9. Percent = IS
100
OF

10. 30% of 80 is what number? % = is unknown
100
25 = x
100 60
Cross multiply to find:
of
100x = 30(80)
When solving for the part, it’s often easier to multiply
the whole by the decimal form of the percent:
80
x .3
24

11. 20% of what number is 30? % = is
100 of
20 = 30
100
x
Cross multiply to find: 20x = 30(100)
20x = 3000 (divide both sides by 20)
x = 150

12. What percent of 200 is 12?
% = is
100 of
x =
100
12
200
200x = 12(100)
200x = 1200
x = 6, so our answer is 6%

14. % = is
100 of
x =
100
36
150

15. 1. What is 45% of 120?
What are we solving for?
First try using mental math to solve
Then set up a proportion
2. 36 is what percent of 30?
3. 48 is 300% of what number?
45 = x
100 120
x =
100
36
30