100 percent of which number is 20?

Let the rquired number be 'P'

According to the question,

$$\begin{gathered} 100 x P 100 = 20 \\ = > P = 20 x 100 100 = 20 \end{gathered}$$

Hence, 100 percent of the number 20 is 20.

Now, you can also try for

20 percent of what number is 100

$$\begin{gathered} 20 x P 100 = 100 \\ = > P = 100 x 100 20 = 500 \\ = > P = 500 \end{gathered}$$

Hence, 20 percent of the number 500 is 100.