Finding a Percent of a Number

10% of a number is that number divided by 10. It is the easiest percent there is.

Build from ten

30% is three lots of 10%. 5% is half of 10%. 35% is 30% plus 5%.

One percent when you need it

1% is the number divided by 100, which builds any percent at all.

Check the size

A percent under 100 gives an answer smaller than the original. That catches most errors.

Start with ten percent

10% of any number is that number divided by 10 — just shift the digits one place right. 10% of 240 is 24. From there, 20% is double that, 5% is half, and 1% is 10% divided by ten. Almost any percentage can be built from these.

Building an awkward percentage

35% of 240 is 10% + 10% + 10% + 5% = 24 + 24 + 24 + 12 = 84. Or 25% (a quarter) plus 10%: 60 + 24 = 84. Both routes agree. Building from friendly pieces is faster than any formula and it can be done mentally.

The direct method

Convert the percentage to a decimal and multiply: 0.35 × 240 = 84. This is what a calculator does and it is the method to use for awkward numbers. Knowing both the building method and the direct one lets you choose.

Check against a benchmark

35% is a bit over a third, and a third of 240 is 80, so expect something near 80. The answer 84 fits. Benchmarking against a half, a quarter or a third catches decimal-point errors, which are the main hazard in percentage work.