Any percentage, starting from 10%

Find 10% by moving the decimal, then build everything else from it.

The question

What is 15% of 240?

The trick

Move the decimal point one place left to get 10%. Halve that for 5%, double it for 20%. Then add or subtract the pieces you need.

Worked example

110% of 240 = 24 (move the decimal one place left)
25% is half of 10%, so 5% of 240 = 12
315% = 10% + 5% = 24 + 12 = 36

So: 36

Remember it like this

10% is one decimal step to the left. Halve it for 5, double it for 20 — then stack the blocks you need.

In the exam

Write the 10% value on your rough sheet first and circle it. Almost every percentage in the paper can be built from it, so you only do the hard step once.

Why it works

Percentages add the same way ordinary numbers do. Once you have the 10% building block, every other percentage is just a combination of halves and doubles of it.

Explain this to my childGet the words to teach it, in your language

Try it yourself

0/5 correct

1
15% of 480
15% of 480
2
20% of 350
20% of 350
3
5% of 640
5% of 640
4
30% of 120
30% of 120
5
25% of 80
25% of 80