What's 8% of 25, without a calculator? It looks awkward, until you flip it.
Flip it
8% of 25 is the same as 25% of 8. And 25% is a quarter, so a quarter of 8 is 2. That means 8% of 25 is 2 as well.
Why does that work?
"Per cent" means "out of a hundred", and "of" means multiply. So:
- 8% of 25 is 8 × 25 ÷ 100
- 25% of 8 is 25 × 8 ÷ 100
Same numbers, multiplied in a different order. Same answer. Picture an 8 by 25 rectangle: turn it round and it's a 25 by 8 rectangle with exactly the same area.
When to use it
You can always flip a percentage question, so pick the side that's easier. Friendly percentages are 50% (halve it), 25% (quarter it) and 10% (divide by 10).
Another example: 16% of 50
Flip it to 50% of 16. Half of 16 is 8. So 16% of 50 is 8. Handy on the non-calculator paper.
What's 12% of 50?
Show the answer
Flip it to 50% of 12. Half of 12 is 6.
Save this for your next test
- x% of y = y% of x.
- "Per cent" means out of 100; "of" means multiply.
- Flip the question and do the easier side.
- Look for 50%, 25% or 10%.
Read the video transcript
- What's 8% of 25? No calculator.
- Sounds hard. But there's a switch that makes it easy.
- Flip it. 25% of 8.
- 25% is a quarter. A quarter of 8 is 2.
- So 8% of 25 is 2 as well.
- But why does that work?
- "Per cent" means "out of a hundred", and "of" means multiply.
- So 8% of 25 is 8 times 25, divided by 100.
- And 25% of 8 is 25 times 8, divided by 100.
- Same numbers, multiplied in a different order. Same answer.
- So you can always flip it, and pick the side that's easy.
- Try another. 16% of 50.
- Flip it. 50% of 16. Half of 16 is 8.
- Handy on the non-calculator paper.
- So, what's 12% of 50? Tell me in the comments.
- Want maths that finally makes sense? Book a free trial lesson at bloomeducationonline.com.
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