If the radius of a sphere is increased by 3.5 cm, its…

If the radius of a sphere is increased by 3.5 cm, its surface area increases by 550 cm². What was the original radius of the sphere? (use $π = {22\over7}$ )

Show answer & explanation

Correct answer: A

Explanation

The correct answer is option 1 i.e. 4.5 cm.

We know,

The total surface area of sphere = 4πr²

Now,

Let r be the radius of the initial sphere

According to the question;

⇒ 4π(r + 3.5)² - 4πr² = 550

⇒ 49π + 28πr = 550

⇒ 7 + 4r = 25

⇒ 4r = 18

⇒ r = 4.5

SSC CHSL 2024 PYQ — Question 61