Two right circular cylinders have their radii in the ratio 2 : 3 and their heights in the ratio 5 : 4. What is the ratio of their volumes?

Volume = π$r^2$h, so the ratio = $(2^{2}x5):(3^{2}x$ 4) = 20 : 36 = 5 : 9. The trap 5 : 6 comes from $2\times 5:3\times 4=10$ : 12 with the radius never squared; 10 : 27 cubes the radii, $8\times 5:27\times 4$, which would suit spheres and not cylinders; 25 : 24 squares the heights instead of the radii.