Percents

1
Percents

• TEKS 6.3B
• Lesson 1 (4th 6 Weeks)

2
Percents

• A special ratio that compares a number to 100
  using the symbol
• Literally means per hundred

3
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.

4

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

25
50
or 25

100
200
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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.

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Example
35

• 35
• Which we read as thirty-five hundredths
• Which written as a decimal is 0.35
• Therefore 35

100
35
0.35
100
7

• Of course can be simplified by
• dividing both the numerator (35) and the
  denominator (100) by 5

35
100
35
5
7


100
5
20
8
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

8
10
80
100
80
100
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• 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
10
Dr Pepper (DP)

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

To move from a decimal we move the decimal point
two places to the right.
D P
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To move from a percent to a decimal, we drop the
percent add the decimal. Then we move it two
places to the left.
D P
12
Examples
1

• Change to a percent.

3
0
.3
3
First lets change the fraction to a decimal.
3
1
0
.0
9
-
1
0
9
-
1
13

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

0
.
3
3

D P
Drop the decimal and add a sign.
14

• Lets change 12.5 into a decimal.

D P
We are going to drop the percent and move the
decimal point two places to the left starting
where the decimal point already is.
2
5
1
.

15

• Lets change 0.2 to a percent.

D P
We are going to move the decimal two places to
the right. Drop the decimal and add a percent
sign.
0
2
0
.

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

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

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We know percents are based out of 100. So we are
going to subtract 28 from 100.
1
0
0
1
1
8
2
-
2
7
17

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

100.
72
2
36
2
18




100
2
50
2
25
But we can reduce.