Question

10.5% of what number is 420?

Answer 1

Number is 4000.

Explanation:

Let the number be `x`.

`therefore` `x(105/1000) = 420`
`rArr` `x = (cancel420 * 1000)/cancel105 = (4 * 1000) = 4000`

Answer 2

`10.5%` of 4000 is `420`

Explanation:

We know that `10.5%` of the number we will call `N` is `420`.
We know that `100` of the number is `N`.

So now we can equate the two lines above by following what we have written:

`10.5/100 = 420/N`

Then cross multiply:

`10.5N = 100*420`

`cancel(10.5)N = 100*cancel(420)4`

`N = 4000`

To check this answer we can calculate `10% or 1/10 of 4000 = 400`

which is reasonably close to the `10.5%` being `420` as given above.