How to Flip a Percentage: A% of B Is B% of A

A% of B equals B% of A — pick whichever side is easier.

8% of 50 = 4

How do you work out an awkward percentage quickly?

A% of B always equals B% of A, so flip to whichever side is easier. For 8% of 50, flip it to 50% of 8, which is half of 8, or 4. It works because both mean the same multiplication: 8% of 50 is 8 × 50 ÷ 100, 50% of 8 is 50 × 8 ÷ 100, and the order of the factors does not change the product. The flip helps whenever one of the two numbers is a friendly percentage like 10, 20, 25 or 50. 16% of 25 becomes 25% of 16, which is a quarter of 16, or 4. 4% of 75 becomes 75% of 4, which is 3. When neither side is friendly, the flip does not help, and splitting is faster: 7% of 30 is 7 × 3 tenths, which is 2.1. Check any answer by multiplying the two numbers and dividing by 100: 16 × 25 = 400, and 400 ÷ 100 = 4.

  1. 8% of 50 = 8 × 50 ÷ 100multiplication is commutative= 50 × 8 ÷ 100 = 50% of 8

    8% of 50 is 8 × 50 ÷ 100. Swap the factors and it reads 50% of 8.

  2. of 840%25%50%75%100%50%

    50% of 8 is half of 8: 4. When the percent is ugly and the number friendly, flip.

Your turn

Three to try in your head — tap what you get.

20% of 50

10% of 50

6% of 50

Keep practicing free in Math Challenge

All 36 shortcuts: the Magic Tricks library.