The ratio of volumes of two spheres A and B is 27 : 125. If the sum of their radii is 56 cm, then find the surface area of A?
Answer & explanation
Correct answer: option 2
A : B
Ratio of volumes \(\frac{4}{3}\) \(\pi \) rA3 : \(\frac{4}{3}\) \(\pi \) rB3
⇒ rA3 : rB3 = 27 : 125
⇒ rA : rB = 3 : 5
sum of radius (rA + rB) = 32 cm
⇒ 8x = 56 cm
⇒ x = 7
rA = 3 × 7 = 21 cm
surface area = 4\(\pi \)r2
= 4 × \(\frac{22}{7}\) × 21 × 21 = 5544 cm2