Step by step
The question
Question: 84 is 21% of what number?
21% of ? = 84
We write it like this: 21% of the number is 84.
84 is a part.
The whole number is what we want.
? = the whole number
Careful!
Many people work out 21% of 84.
But 84 is not the whole.
It is only 21% of it.
Careful: not 21% of 84 ✗
1 Find 1%
21% is 21 lots of 1%.
So we find 1% first.
21% = 21 × 1%
1% is 84 divided by 21: 4.
1% of ? = 84 ÷ 21 = 4
2 Find 100%
The whole number is 100%: 100 lots of 1%.
100% = the whole
4 times 100 is 400.
100% of ? = 4 × 100 = 400
So 84 is 21% of 400.
3 Check
Let's check: is 21% of 400 really 84?
21% is 21/100.
Of means times.
21% of 400 = 21100 × 400
400 divided by 100 is 4.
21 times 4 is 84.
= 21 × 4 = 84 (400 ÷ 100 = 4)
We get 84.
So it is right!
Let's look back.
First: find 1%.
Then: find 100%.
Last: check.
Answer
100% of ? = 4 × 100 = 400