This ppt include percentage and examples

1. Percentages
A percent is a ratio of a number to 100. The symbol % is used to
indicate a percent.
The word percent means “per hundred.”
So 6% means “6 out of 100.”

2. 6
100
= 6%
Example
Notice the 10 x 10 square grid. There are
100 total squares. Six of the squares are
colored. Six red squares of 100 total
squares can be shown like this:

3. Which of the following is an example of a percent?
32%
A B
76

4. Additional Example 3: Writing Percents as Decimals
Write 31% as a decimal.
Method 1
Use pencil and paper.
31% = 31
100
= 0.31
Write the percent as a fraction with a
denominator of 100.
Divide 17 by 100.
Method 2 Use mental math.
31% = 0.31 Move the decimal point two places
to the left.

5. Percentages
Percentage increase
Find the percentage of the quantity and add it to the original
Example 1:
Increase 300 by 12% 12 × 300
100
3
= 36
cancel common factors
200 + 36 = 236
Example 2:
Increase 170 by 30%
cancel common factors
170 + 51 = 221
30 × 170
100
3
10
≡
= 51

6. Percentages
Percentage increase
Find the percentage of the quantity and add it to the original
Example 1:
Increase 300 by 12% 12 × 300
100
3
= 36
cancel common factors
200 -36 = 164
Example 2:
Increase 170 by 30%
cancel common factors
170 -51 = 119
30 × 170
100
3
10
≡
= 51

7. Percentages
Percentage increase
When calculating a percentage increase of a quantity we are
starting with 100% and then we add the percentage asked for.
e.g. Increase a quantity by 23%
100 % + 23 % = 123 %
100 % + 23 % = 123 %
In order to do this calculation we write the percent as a
fraction in hundredths. So this becomes:
100 + 23 = 123
100 100 100
Now 123 = 1.23
100
This is called the
percentage multiplier for
a percentage increase

8. Percentages
Example :
Increase 345 by 56%
the percentage multiplier is 1.56
100 % + 56 % = 156 % 156 = 1.56
100
345 × 1.56 = 538.2

9. Percentages
Now do these:
1. Increase 125 by 16%
2. Increase 340 by 9%
3. Increase 575 by 22%
4. Increase 84 by 1.3%
5. Increase £6.30 by 17.5%
Percentage multiplier is 1.16
125 × 1.16 = 145
Percentage multiplier is 1.09
340 × 1.09 = 370.6
Percentage multiplier is 1.22
575 × 1.22 = 701.5
Percentage multiplier is 1.013
80 × 1.013 = 81.04
Percentage multiplier is 1.175
6.30 × 1.175 = £7.40

10. Percentages
Percentage decrease
When calculating a percentage decrease of a quantity we are
starting with 100% and then we subtract the percentage asked for.
e.g. decrease a quantity by 23%
100 % - 23 % = 77 %
100 % - 23 % = 77 %
In order to do this calculation we write the percent as a
fraction in hundredths. So this becomes:
100 - 23 = 77
100 100 100
Now 77 = 0.77
100
This is called the
percentage multiplier for
a percentage decrease

11. Percentages
Example :
Decrease 345 by 56%
the percentage multiplier is 0.44
100 % - 56 % = 44 % 44 = 0.44
100
345 × 0.44 = 151.8

12. Percentages
To summarise percentage calculations
Original quantity × percentage multiplier = new quantity
By understanding how to rearrange equations you can find any
of the three if you know the other two.