Question

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 is
(a) 540
(b) 450
(c) 380
(d) 472

Answer 1

(b) 450

Number of coins = $\frac{\mathrm{volume}\mathrm{of}\mathrm{cylinder}\mathrm{to}\mathrm{be}\mathrm{formed}}{\mathrm{volume}\mathrm{of}\mathrm{a}\mathrm{coin}}$

$$\begin{gathered} =\frac{\mathrm{\pi }\times 2.25\times 2.25\times 10}{\mathrm{\pi }\times 0.75\times 0.75\times 0.2} \\ =\frac{225\times 225\times 5}{75\times 75} \\ =450 \end{gathered}$$