Question:
Note Take $\pi=\frac{22}{7}$, unless stated otherwise.
A hemispherical bowl made of brass has inner diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of ₹ 32 per 100 cm2.
Solution:
Inner radius of the bowl, $r=\frac{10.5}{2}=5.25 \mathrm{~cm}$
$\therefore$ Inner curved surface area of the bowl $=2 \pi r^{2}=2 \times \frac{22}{7} \times(5.25)^{2}=173.25 \mathrm{~cm}^{2}$
Rate of tin-plating $=₹ 32$ per $100 \mathrm{~cm}^{2}$
∴ Cost of tin-plating the bowl on the inside
= Inner curved surface area of the bowl × Rate of tin-plating
$=173.25 \times \frac{32}{100}$
$=₹ 55.44$
Thus, the cost of tin-plating the bowl on the inside is ₹ $55.44$.