A sum is being lent at 20 % per annum compound interest.what is the ratio of increase in amount of 4th year to 5th year?

$\frac{P1+\frac{r}{100}4}{P1+\frac{r}{100}5}=\frac{1}{1+\frac{r}{100}} =\frac{100}{100+r}=\frac{100}{120}=\frac{5}{6}$