Percents

TEKS 6.3B

Lesson 1 (4th 6 Weeks)

Percents

• A special ratio that compares a number to 100 using the symbol %

• Literally means “per hundred”

Examples:

• If you have 100 marbles and 35 of them are red, then 35% are red

• If you use 25 out of 100 postage stamps, then you used 25% of your stamps.

• If you used 50 out of 200 postage stamps, you used 25% of your stamps.

50 or 25%=10025

200

Representing Percents As Fractions and Decimals

• A number followed by a percent symbol (%) has a denominator of 100 and can be easily written as a fraction or a decimal.

Example:

• 35% =

• Which we read as “thirty-five hundredths

• Which written as a decimal is 0.35• Therefore: 35% =

35100

35100

= 0.35

• Of course can be simplified by

dividing both the numerator (35) and the denominator (100) by 5

35100

35100÷5

5720=

Decimal to Percent Example

• 0.8 is read as “eight tenths and is written as the fraction (ratio)

which is equivalent to

• compares 80 to 100 and can be

written as 80%

810

80100

80100

•Or we can change a decimal to a percent by moving the decimal point two places to the right and adding the % symbol

0.8 =

0.80 =80%

Dr Pepper (DP)

• An easy way to remember which way to move the decimal and how many times, is to remember Dr Pepper.

D PTo move from a decimal we move the decimal point two places to the right.

D P

To move from a percent to a decimal, we drop the percent & add the decimal. Then we move it two places to the left.

Examples:

• Change to a percent.13

First let’s change the fraction to a decimal.

3 1 0.00.3

9-10

3

9-1

• Now we have the decimal lets change it to a percent

0. 33 %Drop the decimal and add a % sign.

D P

• Let’s change 12.5% into a decimal.

2 51 . We are going to drop the percent and move the decimal point two places to the left starting where the decimal point already is.

D P%

• Let’s change 0.2 to a percent.

0

D P20. %

We are going to move the decimal two places to the right. Drop the decimal and add a percent sign.

We are going to add a 0 by the two to hold the place of the ones place.

Last One

• 28% of the class failed last weeks pop quiz. Write how many did not fail the quiz as fraction.

We know percents are based out of 100. So we are going to subtract 28 from 100.

18

0 2

0-

19

1

27

• Now we can change 72% to a fraction. Remember fractions are based off of100.

But we can reduce.

72100

22÷ =36

50 ÷22 = 18

25