Fractions to percentages on sight

Learn eight fractions and you can convert almost anything.

The question

What is 3/8 as a percentage?

The trick

Memorise the unit fractions — 1/2 = 50%, 1/3 ≈ 33.33%, 1/4 = 25%, 1/5 = 20%, 1/6 ≈ 16.67%, 1/8 = 12.5%, 1/10 = 10%, 1/20 = 5% — then multiply by the top number.

Worked example

11/8 = 12.5%
2You need three of them: 12.5 × 3
33/8 = 37.5%

So: 37.5%

Remember it like this

Halve your way down: 1/2 is 50, half of that is 25 for 1/4, half again is 12.5 for 1/8. Each halving of the fraction halves the percentage.

In the exam

Write the eight-value table in the margin the moment the exam starts, while your memory is fresh. Fraction–percentage conversions turn up in ratio, profit-loss and statistics questions alike.

Why it works

Every fraction is just a count of unit fractions. Once you know what one eighth is worth, three eighths is simple multiplication.

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Try it yourself

0/4 correct

1
1/4 as a percentage
1/4 as a percentage
2
3/4 as a percentage
3/4 as a percentage
3
1/5 as a percentage
1/5 as a percentage
4
5/8 as a percentage
5/8 as a percentage