# Surface Areas & Volumes | Exercise 13.4 | Q5

###### NCERT Solutions for Class 9 Math | Curved Surface Area of Hemisphere

Question 5: 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 Rs.16 per 100 cm2.

## NCERT Solution to Class 10 Maths

### Explanatory Answer | Exrecise 13.4 Question 5

#### Step 1: Compute Curved Surface Area of Bowl

Diameter of the hemispherical bowl, d = 10.5 cm
Radius of the hemispherical bowl, r = $\frac{d}{2}$ = $\frac{10.5}{2}$ cm
Curved surface area of hemisphere = 2 × π × r2
Take π = $\frac{22}{7}$
Curved surface area of the hemispherical bowl = 2 × $\frac{22}{7}$ × $\frac{10.5}{2}$ × $\frac{10.5}{2}$
= 11 × 1.5 × 10.5
= 173.25 cm2

#### Step 2: Compute the Cost of Tin-plating the Bowl

Cost of tin-plating the hemispherical bowl per 100 cm2 = Rs. 16
Cost of tin-plating the hemispherical bowl per cm2 = Rs. 0.16
Cost of tin-plating the bowl on inside at the rate of Rs.0.16 per cm2= 173.25 × 0.16
= Rs.27.72

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