answer: 21 is 70% of 30
Working out percentages
We have, 70% × x = 21
or, 70100 × x = 21
Multiplying both sides by 100 and dividing both sides by 70,
we have x = 21 × 100
70
x = 30
If you are using a calculator, simply enter 21×100÷70, which will give you the answer.