Chapter 2

Percentages

Percent means out of 100 — find percentages and change between forms.

What percentage means

Percent means 'out of 100'. So 25% means 25 out of 100. Percentages, fractions and decimals are three ways to show the same amount: 50% = ½ = 0.5.

Key idea

To find a percentage of a number, change the percent to a fraction over 100, then multiply by the number.

Worked example

Worked example

Find 25% of 80.
25% = 25/100 = ¼.
¼ of 80 = 80 ÷ 4 = 20.

Changing between forms

To change a decimal to a percentage, multiply by 100: 0.5 = 50%. To change a fraction, first make an equal fraction over 100: ¼ = 25/100 = 25%. Some percentages are worth learning by heart because they appear often: 50% is one half, 25% is one quarter, and 10% is found by dividing the number by 10. These help with everyday sums like a shop discount or a test score out of 100.

Remember

  • Percent means 'out of 100'.
  • 50% = ½, 25% = ¼, 75% = ¾.
  • Percentage of a number: divide by 100, then multiply.

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