A hemispherical brass bowl has inner-diameter 10.5 cm. Find the cost of tin-plating it on the inside at the rate of ₹ 16 per 100 cm².

Given, internal diameter = 10.5 cm.

Internal radius = $\dfrac{\text{Internal diameter}}{2}$

= $\dfrac{10.5}{2} = 5.25$ cm.

Internal curved surface area of hemispherical shell = 2πr².

Putting values in equation we get,

Internal curved surface area of hemisphere = 2 x $\dfrac{22}{7}$ x (5.25)²

$= \dfrac{2 \times 22 \times 27.5625}{7} \\[1em] = \dfrac{1212.75}{7} = 173.25 \text{ cm}^2.$

The cost of tin-plating it on the inside at the rate of ₹ 16/100 cm² or ₹ 0.16/cm².

∴ Cost of tin-plating 173.25 cm² = 173.25 × 0.16 = ₹ 27.72.

Hence, the cost of tin-plating = ₹ 27.72.