1. WEEK 4
Finding Percenatages
Percentage increase & decrease

2. STARTER
On your notebook, write the following sets in the ROSTER NOTATION.
{x : x is even and x ≤ 8}
{x : x = 3n, n ∈ N, n ≤ 4}
{x : x = n2, n ≤ 5, n ∈ N}
{x : x is odd}

3. STARTER ANSWERS A = {2, 4, 6, 8} B = {3, 9, 27, 81}
C = {1, 4, 9, 16, 25}
D = {1, 3, 5, } 

4. OBJECTIVES Find percentages of quantities
Interpret percentage as an operator.
Use a multiplier to increase or decrease.

5. What is a percentage?

6. What is a percentage? A percentage is a ratio of a number to 100.
The symbol % is used to indicate a percent.
The word percent means “per cent” , “per hundred.” So 6% means “6 out of 100.”

7. Example
Notice the 10 x 10 square grid. There are 100 total squares. Seven of the squares are colored. Seven red squares of 100 total squares can be shown like this: 7
100
= 7 %

8. Which of the following is an example of a percent?67
23% A B
Which of the following is an example of a percent?

9. Example 1: Modeling Percentage
Write the percent modeled by each grid.
A B.
shaded
total
_______ 32
100
___
shaded
total
_______ 75
100
___
= 32%
= 75%
Steps 9

10. Example 2: Modeling Percentage
Write the percent modeled by each grid.
A B.
shaded
total
_______ 44
100
___
shaded
total
_______ 66
100
___
= 44%
= 66%
Steps

11. Additional Example 3: Writing Percentage as Decimals
Write 21% as a decimal.
Method 1
Use pencil and paper. 21
100
Write the percent as a fraction with a
denominator of 100.
21% =
= 0.21
Divide 21 by 100.
Method 2
Use mental math.
21%
= 0.21
Move the decimal point two places to the left.
I do: How did I calculate the percent to a decimal?

12. Example 1: 34% of 5 = (34/100) x 5 = 1.7 Example 2: 6% of 1.45
Finding Percentages of a number!
Example 1:
34% of 5
= (34/100) x 5
= 1.7
Example 2:
6% of 1.45
= (6/100) x 1.45
= 0.087

13. Finding Percentages of quantities?
Example 1:
21% of 650 AED
= (21/100) x 650
= AED
Example 2:
85% of 38 KG
= (85/100) x 38
= 32.3 KG
Example 3:
Find 3½% of $80
First > Express (7/2)/100 as a fraction = 7/200 = 0.035
Second > (0.035) x (80) = 80/15 = $2.80

14. Increasing and Decreasing Quantities by a Percentage
When increasing or decreasing by a percentage, there are two ways to do this:
Find the actual increase or decrease and add it to, subtract it from the original amount.
Use a simple multiplication
For example, to increase by 20%, multiply by We increase an amount (b AED) by 20%.
The increase is b AED x (20/100) = 0.2 b
So the new price is b AED + 0.2b = ( )b = 1.2b
A 20% increase is the same as to multiply by 1.2 to get the new price.
100% + 20% = 120% = 120/100 = is the multiplier!
A 20% decrease of 20% is the same as:
100% - 20% = 80% = 80/100 = is the multiplier!

15. What is a multiplier? How does it help to increase and decrease the change in percentage?
Example question 1 - Increase AED130 by 20%.
An increase of 20% is an increase from 100% to 120%.
To do this you would multiply by 120/100, which is the same as multiplying by 1.2.
In other words, multiplying an amount by 1.2 is the same as increasing it by 20%.
So the number 1.2 is the multiplier needed to do the calculation, which now looks like this:
AED 130 x 1.2 = AED156, which is the answer.

16. Teacher to go over Example 4.4 & 4.5
(Maths iBook page 72 & 73)

17. CLASSWORK 1
Pair Activity
On your notebook, show an organized solution on the following:
G11 Mathematics Website
WK 4 – L1 CLASSWORK 1 IGCSE Past Paper Questions on Percentage

18. CLASSWORK 2
Individul Activity
On your notebook, show an organized solution on the following:
iBook G11 Maths, page 75 – 76
#’s 1, 2, 3 a, c, f, h, 4, 5, 6

19. HOMEWORK
On your notebook, show an organized solution on the following:
iBook G11 Maths, page 76 #’s 7 & 8
Any classwork NOT finished

20. EXTENSION ACTIVITY
For advanced students:
On your notebook, show an organized solution on the following:
G11 Mathematics Website
WK 4 – L1 Extension Activity 1 Percentage

21. PLENARY
Share one or two things you have learned in today’s lesson

22. THANK YOU! 