Mental Percentages: A Small Toolkit

You do not need a separate trick for every percentage. Build unusual percentages from a few easy anchors.

10% and 1%

10% of 360 = 36. 1% = 3.6. From these two values you can build many others.

5%

Half of 10%. So 5% of 360 = 18.

15%

10% + 5%. For 360: 36 + 18 = 54.

25% and 50%

25% is one quarter; 50% is one half. 25% of 84 = 21.

Estimate before decimals

If the exact number is awkward, first establish the rough size. This catches misplaced decimal points and impossible answers.

Educational note: these techniques are practice methods, not medical or cognitive-performance claims.