The radii of two cylinders are in the ratio 2 : 3 and their heights are in the ratio 5 : 3.

(b) 20 : 27
Let the radii of the two cylinders be 2r and 3r and their heights be 5h and 3h, respectively.

Then, ratio of their volumes $=\frac{\pi \times(2 \mathrm{r})^{2} \times 5 h}{\pi \times(3 r)^{2} \times 3 h}$

$=\frac{4 r^{2} \times 5}{9 r^{2} \times 3}$

$=\frac{20}{27}$

$=20: 27$