# RS Aggarwal Solutions Class 9 Mathematics Solutions for Volume And Surface Area Of Solids Exercise 15D in Chapter 15 - Volume And Surface Area Of Solids

Question 28 Volume And Surface Area Of Solids Exercise 15D

A hemispherical bowl made of brass has inner diameter 10.5cm. Find the cost of tin-plating it on the inside at the rate of ₹ 32 per 100cm2.

It is given that

Inner diameter of the hemispherical bowl = 10.5cm

Inner radius of the hemispherical bowl = 10.5/2 = 5.25cm

We know that

Inner curved surface area of the bowl = 2 πr2

By substituting the values

Inner curved surface area of the bowl = 2 × (22/7) × 5.252

On further calculation

Inner curved surface area of the bowl = 2 × (22/7) × 27.5625

So we get

Inner curved surface area of the bowl = 173.25 cm2

It is given that

Cost of tin plating inside = ₹ 32 per 100cm2

So the cost of tin plating 173.25 cm2 = ₹ (32 × 173.25)/100 = ₹ 55.44

Therefore, the cost of tin plating it on the inside is ₹ 55.44.

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