What you need to know
Per cent means out of 100. A fraction, a decimal and a percentage are just three ways of writing the same amount: 14 = 0.25 = 25%. Converting between them is a skill you will use constantly, from test scores to discounts to interest rates. Learn the benchmark values below and the rest can be worked out from them.
| Fraction | Decimal | Percentage |
|---|
| 12 | 0.5 | 50% |
| 14 | 0.25 | 25% |
| 34 | 0.75 | 75% |
| 15 | 0.2 | 20% |
| 110 | 0.1 | 10% |
| 18 | 0.125 | 12.5% |
| 13 | 0.333… (recurring) | 3313% |
| 23 | 0.666… (recurring) | 6623% |
The six conversions. Decimal to percentage: multiply by 100 (move the decimal point two places right). Percentage to decimal: divide by 100 (two places left). Fraction to decimal: divide the numerator by the denominator. Fraction to percentage: convert to a decimal first, then × 100 (or make the denominator 100 if that is easy). Percentage to fraction: write it over 100 and simplify. Decimal to fraction: use place value (0.35 is 35 hundredths = 35100 = 720).
Convert 38 to a decimal and a percentage
- Fraction to decimal: 3 ÷ 8 = 0.375.
- Decimal to percentage: 0.375 × 100 = 37.5%.
- Sense check: 38 is a bit less than 12, and 37.5% is a bit less than 50%.
Convert 64% to a fraction in simplest form and to a decimal
- Percentage to fraction: 64% = 64100.
- Simplify: the highest common factor of 64 and 100 is 4, so 64100 = [frac 16/25].
- Percentage to decimal: 64 ÷ 100 = 0.64.
Convert 0.06 and 1.5 to percentages
- 0.06 × 100 = 6%. Moving the point two places right turns 0.06 into 6.
- 1.5 × 100 = 150%. Percentages can be more than 100 when the amount is more than one whole.
Order 35, 0.65 and 58% from smallest to largest
- Convert everything to the same form. Decimals are usually easiest.
- 35 = 3 ÷ 5 = 0.6. 58% = 0.58. 0.65 stays as it is.
- Order the decimals: 0.58, 0.6, 0.65.
- Answer in the original forms: 58%, [frac 3/5], 0.65.
Common mistake: 0.5 becoming 5% or 0.06 becoming 60%. Moving the decimal point two places means 0.5 = 0.50 = 50% and 0.06 = 6%. If a percentage looks ten times too big or too small, recount the places.
Common mistake: writing 13 as 0.3 or 30%. 1 ÷ 3 = 0.333… recurring, which is 33.3% (to one decimal place) or exactly 3313%. Rounding too early makes later answers wrong.
Check yourself
- Write 0.45 as a percentage.
- Write 8% as a decimal.
- Write 720 as a percentage.
- Write 0.125 as a fraction in simplest form.
- Write 35% as a fraction in simplest form.
- Which is largest: 23, 0.6 or 65%?
Answers: 1. 45% 2. 0.08 3. 35% (720 = 35100) 4. 18 5. 720 6. 23 (it is 0.666…, which is more than 0.6 and 0.65)