Topic/Skill
Topic: CalculatingDefinition/Tips
with Percentages Example
1. Increase or Non-calculator: Find the percentage and Increase 500 by 20% (Non Calc):
Decrease by a add or subtract it from the original 10% of 500 = 50
Percentage amount. so 20% of 500 = 100
500 + 100 = 600
Calculator: Find the percentage multiplier
and multiply. Decrease 800 by 17% (Calc):
100%-17%=83%
83% ÷ 100 = 0.83
0.83 x 800 = 664
2. Percentage The number you multiply a quantity by to The multiplier for increasing by 12% is
Multiplier increase or decrease it by a percentage. 1.12
The multiplier for decreasing by 12% is
0.88
The multiplier for increasing by 100%
is 2.
3. Reverse Find the correct percentage given in the A jumper was priced at £48.60 after a
Percentage question, then work backwards to find 10% reduction. Find its original price.
100%
100% - 10% = 90%
Look out for words like ‘before’ or
‘original’ 90% = £48.60
1% = £0.54
100% = £54
4. Simple Interest calculated as a percentage of the £1000 invested for 3 years at 10%
Interest original amount. simple interest.
10% of £1000 = £100
Interest = 3 × £ 100=£ 300
Mr A. Coleman Glyn School
Topic: CalculatingDefinition/Tips
with Percentages Example
1. Increase or Non-calculator: Find the percentage and Increase 500 by 20% (Non Calc):
Decrease by a add or subtract it from the original 10% of 500 = 50
Percentage amount. so 20% of 500 = 100
500 + 100 = 600
Calculator: Find the percentage multiplier
and multiply. Decrease 800 by 17% (Calc):
100%-17%=83%
83% ÷ 100 = 0.83
0.83 x 800 = 664
2. Percentage The number you multiply a quantity by to The multiplier for increasing by 12% is
Multiplier increase or decrease it by a percentage. 1.12
The multiplier for decreasing by 12% is
0.88
The multiplier for increasing by 100%
is 2.
3. Reverse Find the correct percentage given in the A jumper was priced at £48.60 after a
Percentage question, then work backwards to find 10% reduction. Find its original price.
100%
100% - 10% = 90%
Look out for words like ‘before’ or
‘original’ 90% = £48.60
1% = £0.54
100% = £54
4. Simple Interest calculated as a percentage of the £1000 invested for 3 years at 10%
Interest original amount. simple interest.
10% of £1000 = £100
Interest = 3 × £ 100=£ 300
Mr A. Coleman Glyn School
