Q135
ArithmeticGeometry & Mensuration
If the radius of a sphere is increased by 2cm, then its surface area increases by 352cm². The radius of the sphere before the increase was
- a.3 cm
- b.4 cm
- c.5 cm
- d.6 cm
Answer: (D) 6 cm
The increase is $4\pi[(r + 2)^2 - r^2] = 16\pi(r + 1) = 352$. With $\pi = \frac{22}{7}$, $r + 1 = 352 \times \frac{7}{352} = 7$, so $r = 6$ cm. A radius of 5 cm would give an increase of only about 302 cm².