Primary 6 Percentage
Start every question by naming the 100%. Then use the given percentage to find the missing amount or work out the change.
Finding the whole from a part and its percentage
When you know a part and the percentage it represents, find 1% first. Multiply that by 100 to get the whole. In a discount question, the sale price is a percentage of the original price.
Given a part directly
$24 is 30% of a sum of money. What is the whole sum?
- Name the whole: the whole sum is 100%.
- Match the part: 30% is $24.
- Find 1%: $24 ÷ 30 = $0.80.
- Find 100%: $0.80 × 100 = $80.
- Check: 30% of $80 is $24.
Answer: $80
Given a price after a discount
A bag costs $60 after a 20% discount. What was its original price?
- Name the whole: the original price is 100%.
- Find the paid percentage: 100% − 20% = 80%.
- Match the part: 80% is $60.
- Find 1%: $60 ÷ 80 = $0.75.
- Find 100%: $0.75 × 100 = $75.
- Check: 20% of $75 is $15; $75 − $15 = $60.
Answer: $75
Try together
45% of a sum is $36. Find the whole sum.
Reveal the answer
$80
Percentage increase and decrease
The original amount is 100%. If the percentage is given, find the change of the original, then add or subtract it. If the original and new amounts are given, compare their difference with the original to find the percentage change.
Percentage increase
A $80 price increases by 15%. What is the new price?
- Name the whole: the original $80 is 100%.
- Find 1%: $80 ÷ 100 = $0.80.
- Find the increase: 15 × $0.80 = $12.
- Add the increase: $80 + $12 = $92.
- Check: the new price is 115% of $80, which is $92.
Answer: $92
Percentage decrease
A $120 price decreases by 25%. What is the new price?
- Name the whole: the original $120 is 100%.
- Find 1%: $120 ÷ 100 = $1.20.
- Find the decrease: 25 × $1.20 = $30.
- Subtract the decrease: $120 − $30 = $90.
- Check: the new price is 75% of $120, which is $90.
Answer: $90
Find the percentage increase
A price rises from $80 to $100. What is the percentage increase?
- Find the increase: $100 − $80 = $20.
- Find the percentage increase: $20$80 × 100 = 25, so the increase is 25%.
- Check: 25% of $80 is $20; $80 + $20 = $100.
Answer: 25% increase
Find the percentage decrease
A price falls from $120 to $90. What is the percentage decrease?
- Find the decrease: $120 − $90 = $30.
- Find the percentage decrease: $30$120 × 100 = 25, so the decrease is 25%.
- Check: 25% of $120 is $30; $120 − $30 = $90.
Answer: 25% decrease
Try together
(a) Increase $200 by 10%. (b) Decrease $80 by 20%. (c) A price rises from $50 to $60. Find the percentage increase.
Reveal the answers
(a) $220 (b) $64 (c) 20% increase