SSC CGL 2020 PYQ — Question 62

The correct answer is option 4 i.e. $\frac{11}{21}$

Let the initial and final radius be 'r' and 'R',

R - r = 2.5........(1)

Increase in their surface area = 110

⇒ 4$\pi$(R² - r²) = 110

⇒ 4 × 22/7 × (R + r)(R - r) = 110

⇒ (R + r)(R - r) = 8.75

⇒ (R + r) = 3.5........(2)

On solving 1 and 2 we get,

R = 3 and r = 0.5

Volume of the sphere = 4/3 × 22/7 × 0.5³ = 11/21 dm³.