Dec. 3, 2013

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