Question

Find the number of coins, 1.5 cm in diameter and 0.2 cm thick, to be melted to form a right circular cylinder with a height of 10 cm and a diameter of 4.5 cm.

Answer 1

Volume of the coin$={\mathrm{\pi r}}^2\mathrm{h}=\frac{22}{7}\times 0.75\times 0.75\times 0.2$
Volume of the cylinder $={\mathrm{\pi r}}^2\mathrm{h}=\frac{22}{7}\times 2.25\times 2.25\times 10$
No. of coins$=\frac{\mathrm{volume}\mathrm{of}\mathrm{cylinder}}{\mathrm{volume}\mathrm{of}\mathrm{coin}}=\frac{2.25\times 2.25\times 10}{0.75\times 0.75\times 0.2}=450\mathrm{coins}$

∴ 450 coins must be melted to form the required cylinder.