Percentages — Mathematics, 11–13
A percentage gives a quantity as parts out of one hundred, making comparisons easier. Mathematics, 11–13 years.
Per cent means out of 100
The word per cent means for each hundred. So 25% means 25 out of every 100, and it is the same amount as 25/100 or 1/4. The symbol % is a short way to write this comparison.
Why percentages help
Fractions with different denominators are hard to compare quickly. A common denominator of 100 gives people a shared scale for test scores, surveys, discounts and changes, so 40% and 60% can be understood at a glance.
Finding a discount
A jacket costs 80 euros and is reduced by 15%. First find 10%: 8 euros. Then find 5%: half of 8 is 4 euros. The discount is 8 + 4 = 12 euros, so the new price is 80 − 12 = 68 euros.
A percentage is not always points
People often say a rise from 50 to 60 is 10%, because the number increased by 10. It increased by 10 percentage points, but the percentage increase is 10 ÷ 50 = 20%. The original amount is the reference.
Percentages in real life
Weather forecasts use percentages for the chance of rain, shops use them for discounts, and batteries use them to show remaining charge. Each number is meaningful only when you know the whole amount it refers to.
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