A cylindrical cube of radius 12 cm contains water upto a depth of 20 cm. A spherical iron ball is dropped into the tub and thus the level of water is raised by 6.75 cm. The radius of the ball is : Pick.
A) 7 cm  B) 8.5 cm  C) 9 cm  D) 9.5 cm  E) None
Sol.   Let the radius of the ball be r cm.   Volume of ball = Volume of water displaced by it.   ∴ 4/3 ∏r³ = ∏ * 12 * 12 * 6.75   ⇒ r³ = 9 * 9 * 9 ⇒ r = 9 cm.   Answer 9 cm
<result>C</result>
A cylindrical cube of radius 12 cm contains water upto a depth of 20 cm. A spherical iron ball is dropped into the tub and thus the level of water is raised by 6.75 cm. The radius of the ball is :