Find the number of coins,
Question:

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

Solution:

Volume of one coin $=\pi \times(1.5)^{2 / 4} \times 0.2$

Volume of cylinder $=\pi \times(4.5)^{2} \times \frac{10}{4}$

So number of coins to be melted

$=\frac{\text { volume of cylinder }}{\text { volume of each coin }}$

$=\left(\frac{4.5}{1.5}\right)^{2} \times \frac{10}{0.2}$

$=9 \times 50$

$=450$