100 percent of which number is 20?

Let the rquired number be 'P'

According to the question,

$\frac{100 x P}{100} = 20=> P = 20 x \frac{100}{100} = 20$

Hence, 100 percent of the number 20 is 20.

Now, you can also try for

20 percent of what number is 100

$\frac{20 x P}{100} = 100=> P = \frac{100 x 100}{20} = 500=> P = 500$

Hence, 20 percent of the number 500 is 100.