SSC CHSL 6 Dec 2015 Shift 1 Paper

Question : 121 of 200

Marks: +1, -0

If the radius of a sphere is increased by 2 cm, then its surface area increases by 352 cm

^2

. The radius of the sphere initially was: (use

π=22/7)

Solution:

Let initial radius = r cm
Initial surface area =

4πr^2

New radius = ( r + 2 ) cm
⇒ New surface area =

4π(r + 2) ^2 = 4πr^ 2 + 352

⇒

4πr ^2 + 16πr + 16π

= 4πr^ 2 + 352

⇒

16π(r + 1) = 352

⇒

(r + 1) =352 / 16 × 7/22

⇒

(r + 1) = 7

⇒

r = 7 − 1 = 6

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