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.
Solution:
Volume of the coin $=\pi \mathrm{r}^{2} \mathrm{~h}=\frac{22}{7} \times 0.75 \times 0.75 \times 0.2$
Volume of the cylinder $=\pi \mathrm{r}^{2} \mathrm{~h}=\frac{22}{7} \times 2.25 \times 2.25 \times 10$
No. of coins $=\frac{\text { volume of cylinder }}{\text { volume of coin }}=\frac{2.25 \times 2.25 \times 10}{0.75 \times 0.75 \times 0.2}=450$ coins
$\therefore 450$ coins must be melted to form the required cylinder.