Aman's income is 20% less than that of Anil.

Let Anil's income be $x$.

Then, Aman's income $=x-\frac{20 x}{100}$

$=\frac{8 x}{10}$

Difference in the incomes of Anil and Aman $=x-\frac{8 x}{10}$

$=\frac{2 x}{10}$

$\therefore$ Percentage of the difference in the incomes of Anil and Aman to that of Aman's incom $e=\left(\frac{2 x}{10}\right) /\left(\frac{8 x}{10}\right)$$\times 100$

$=\frac{1}{4} \times 100$

$=25 \%$