Percent of a Number

A percentage is a fraction out of 100. To find a percentage of a number, multiply the number by the percentage divided by 100.

What Is a Percent?

"Per cent" means per hundred. 40% means 40 out of 100, or $\frac{40}{100} = 0.4$ .

A percent bar showing 40 out of 100 shaded in blue.

Finding a Percent of a Number

Percent of a Number

P\% \text{ of } N = \frac{P}{100} \times N

Convert percent to a decimal (divide by 100), then multiply.

Method 1 — Decimal: $30\% \text{ of } 80 = 0.30 \times 80 = 24$

Method 2 — Fraction: $30\% \text{ of } 80 = \frac{30}{100} \times 80 = \frac{2400}{100} = 24$

Finding the Whole from a Part

If 25% of a number is 15, what is the number?

$\text{Number} = \frac{15}{25} \times 100 = 60$

Tip The 10% trick: 10% of any number = number ÷ 10. Then double for 20%, halve for 5%.

Common Percents

Percent	Fraction	Decimal
10%	1/10	0.1
25%	1/4	0.25
50%	1/2	0.5
75%	3/4	0.75
100%	1	1.0

A jacket costs €60. It is on sale for 15% off. What is the discount?

$15\% \text{ of } 60 = 0.15 \times 60 = 9\text{ EUR}$

Sale price: €60 − €9 = €51

Real-World Examples

Real world: shopping discount

A €60 jacket is on sale at 15% off.

$15\% \text{ of } 60 = 0.15 \times 60 = 9\text{ EUR saved}$

Sale price: €60 − €9 = €51. Retailers display discounts as percentages; calculating the actual saving helps you compare deals across different shops.

Real world: test score

A student scores 36 out of 40 in a test.

$\frac{36}{40} \times 100 = 90\%$

Schools, universities, and employers use percentage scores to rank and compare performance fairly across different test formats.

Real world: food nutrition label

A 35 g cereal bar lists 12% sugar on its label.

$12\% \text{ of } 35 = 0.12 \times 35 = 4.2 \text{ g of sugar}$

Nutritionists and health-conscious shoppers convert percentage figures to grams to understand what they are actually consuming.

Practice Problems

What is 35% of 200?

Show answer

0.35 × 200 = 70.

20% of a number is 14. What is the number?

Show answer

14 / 0.20 = 70.