Surface Areas & Volumes | Exercise 13.4 | Q8

CBSE Class 9 Maths | NCERT Solution to Exercise | Surface Area of Hemisphere

Question 8: A hemispherical bowl is made of steel, 0.25 cm thick. The inner radius of the bowl is 5 cm. Find the outer curved surface area of the bowl.

NCERT Solution to Class 10 Maths

Explanatory Answer | Exercise 13.4 Question 8

Given Data:
1. Thickness of the hemispherical bowl = 0.25 cm
2. Inner radius of the bowl, r1 = 5 cm

∴ outer radius of the hemispherical bowl, r2 = Inner radius + Thickness
= 5 + 0.25
= 5.25 cm = $\frac{10.5}{2}$ = $\frac{21}{4}$

Outer curved surface area of hemisphere = 2 × π × r22
Take π = $\frac{22}{7}$
Outer curved surface area of hemisphere = 2 × $\frac{22}{7}$ × $\frac{21}{4}$ × $\frac{21}{4}$
= 2 × 22 × $\frac{3}{4}$ × $\frac{21}{4}$
= 11 × 3 × $\frac{21}{4}$
= $\frac{693}{4}$ = 173.25

Outer curved surface area of hemispherical bowl = 173.25 cm2

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