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

Answer: Option C

Volume one coin :
$$\begin{array}{rl}& =\left(\frac{22}{7}\times \frac{75}{100}\times \frac{75}{100}\times \frac{2}{10}\right)\text{c}{\text{m}}^3\\ & =\frac{99}{280}\text{ c}{\text{m}}^3\end{array}$$
Volume of larger cylinder :
$$=\left(\frac{22}{7}\times \frac{9}{4}\times \frac{9}{4}\times 10\right)\text{ c}{\text{m}}^3$$
Number of coins :
$$\begin{array}{rl}& =\left(\frac{22}{7}\times \frac{9}{4}\times \frac{9}{4}\times 10\times \frac{280}{99}\right)\\ & =450\end{array}$$