Fractions and percentages by hand

Divide by the bottom number, then multiply by the top number.

1. 3/8 of 240 g
2. 240 ÷ 8 = 30
3. 30 × 3 = 90 g

Start from 10% (divide by 10). Halve it for 5%, halve again for 2.5%, and divide by 100 for 1%. Add the pieces you need.

1. 35% of 260
2. 10% = 26, so 30% = 78
3. 5% = 13
4. 35% = 78 + 13 = 91

1. 17.5% of £80
2. 10% = 8, 5% = 4, 2.5% = 2
3. 17.5% = 8 + 4 + 2 = 14, so £14

To increase by a percentage, work out the percentage and add it on. To decrease, take it away.

To turn a fraction into a decimal, make the bottom 10, 100 or 1000, or divide the top by the bottom.

1. 7/20
2. 7/20 = 35/100
3. 35/100 = 0.35 = 35%

To turn a decimal into a fraction, write it over 10, 100 or 1000, then simplify: 0.45 = 45/100 = 9/20.

To compare a mix of fractions, decimals and percentages, write them all as percentages first. 3/5 = 60%, 0.58 = 58%, so 3/5 is bigger than 0.58.

Cover the right-hand side and say each one: 1/2 = 0.5 = 50%, 1/4 = 0.25 = 25%, 3/4 = 0.75 = 75%, 1/5 = 0.2 = 20%, 1/8 = 0.125 = 12.5%, 1/20 = 0.05 = 5%. Most non-calculator conversions are built from these.