Percentages

1
Percentages
Objectives B Grade Work out reverse percentage
problems
Prior knowledge
Understand
Finding percentages of quantities calculator
and non calculator
Percentage increase / decrease percentage
multipliers
Rearranging equations
2
Percentages
The method of working out percentage increase /
decrease is
Original quantity percentage multiplier new
quantity
Reverse percentage problems will give the new
quantity and you need to work out the original
quantity
To calculate the original quantity we rearrange
the equation
Original quantity
percentage multiplier
new quantity

3
Percentages
Example 1
Irene paid 38.70 for a skirt that had been
reduced by 10 a sale. What was the original
price?
Original quantity 0.9 38.70
Original quantity 38.70 0.9
Original quantity 43
4
Percentages
Example 2
Jack received a 3.5 pay rise. His new salary is
12 420
Original quantity 1.035 12 420
Original quantity 12420 1.035
Original quantity 12 000
5
Now do these 1. A quantity is decreased by
3. It is now 38.8. What was the original
value? 2. A coat was advertised in a
sale at 79 after a 5 reduction. What was the
original price? 3. Nobbys salary was
increased by 7. His new salary after the pay
rise is 28 890. What was his original salary?
4. In a local election Labour received 1375
votes. This was 12 up on the previous election.
What was their previous number of votes.
5. A charitys income has been reduced by 12.5.
Its income is now 49 000 per year. What was
its previous revenue
Percentages
38.8 0.97
40
79 0.95
83.16
28890 1.07
27 000
1228
1375 1.12
49000 0.875
56 000