What is X percent of Y?
Type the two numbers and the answer appears, with the sum written out underneath.
What is X% of Y?
What is of ?
Working: 80 × 15 ÷ 100 = 12
X is what percent of Y?
is what percent of ?
Working: 12 ÷ 80 × 100 = 15%
X is Y% of what?
Works backwards from a part to the whole.
is of what?
Working: 12 × 100 ÷ 15 = 80
How to work out a percentage of a number
Multiply the number by the percentage, then divide by 100. 15% of 80 is 80 × 15 ÷ 100 = 12.
The order doesn't matter, so 15% of 80 is the same as 80% of 15. That helps in your head: 8% of 50 is 50% of 8, which is 4.
The other two questions
“12 is what percent of 80?” divides the part by the whole: 12 ÷ 80 × 100 = 15%. “12 is 15% of what?” runs it backwards: 12 × 100 ÷ 15 = 80. It's one sum, rearranged three ways.
Doing it without a calculator
10% moves the decimal point one place left, so 10% of 80 is 8. Half of that is 5%, which is 4. 1% moves the point two places: 0.8. Most percentages can be built from those. 15% of 80 is 8 + 4 = 12, and 18% would be 12 + 0.8 + 0.8 + 0.8 = 14.4.