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1. 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.

A. 430

B. 440

C. 450

D. 460

Solution:

Volume one coin :

\begin{aligned} = (\frac{22}{7} \times \frac{75}{100} \times \frac{75}{100} \times \frac{2}{10}) c m^{3} \\ = \frac{99}{280} c m^{3} \end{aligned}

Volume of larger cylinder :

= (\frac{22}{7} \times \frac{9}{4} \times \frac{9}{4} \times 10) c m^{3}

Number of coins :

\begin{aligned} = (\frac{22}{7} \times \frac{9}{4} \times \frac{9}{4} \times 10 \times \frac{280}{99}) \\ = 450 \end{aligned}

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