RBI Grade B Officers 2017 jun Paper

3) Let the radius of water poolbe R feet.
Radius of water pool with wall= (R + 4) feet
Area of the concrete wall
=π[(R+4)2−R2]
= • [(R + 4 +R) (R + 4 – R)
= 8π (R + 2) sq. feet
∴8π(R+2)=

11

25

πR2
⇒11R2=200(R+2)
⇒11R2–200R–400=0
⇒11R2–220R+20R–400=0
⇒ 11R (R – 20) + 20(R – 20)= 0
⇒ (R – 20) (11R + 20) = 0
∴ R = 20 feet