SSC MTS 2026 PYQ — Question 7

Outer radius = 36/2 = 18 cm
Inner radius = 28/2 = 14 cm
Radius of the ball = 2 cm
Volume of the hollow sphere$= \frac{4}{3} \pi (R^3 - r^3)$
Volume of a solid sphere = (4/3)πa³
Surface area of ​​a solid sphere = 4πa²
Volume of the shell $= \frac{4}{3} \pi (18^3 - 14^3) = \frac{4}{3} \pi (3088)$
Volume of one ball $= \frac{4}{3} \pi (2^3) = \frac{4}{3} \pi (8)$
Number of balls = 3088 / 8 = 386
Surface area of ​​one ball = 4π(2²) = 16π
Total surface area of ​​all balls = 386 × 16π = 6176π
Number of balls = 386