Lesson 4 of 11
One amount said as a percentage of another
Show on a big screenYou score 18 marks on a test out of 24. The register wants a percentage.
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Step 1 of 3
- Whole is 24. Part is 18.
- Divide: 18 ÷ 24 = 0.75.
- On a 0-to-100 scale, that is 75%.
The rule
The part is the piece you want to measure: here 18. The whole is the full total: here 24.
Write the part over the whole. Divide. Then multiply by 100. Dividing gives a decimal. Because per cent counts hundredths, multiply it by 100.
The whole is what you compare against. Swap the part and the whole, and the answer changes. The two answers match only when part and whole are equal.
- 20 of 25 notebooks sold: 20 ÷ 25 = 0.8. Then 0.8 × 100 = 80, so 80%.
- Part 25, whole 20: 25 ÷ 20 = 1.25. Then 1.25 × 100 = 125, so 125%.
Watch out!
24 − 18 = 6 is the gap. It is not 6%. Six out of 24 is 25%.
Try the lab to finish this lesson.