Chapter: Mensuration· Mathematics Part 2 (Geometry)
Answer: Radius of the ball = 9 cm
Volume of the ball = volume of water raised (a cylinder of radius 12 cm and height 6.75 cm).
\(\dfrac{4}{3}\pi r^3 = \pi \times 12^2 \times 6.75\)
\(\therefore r^3 = \dfrac{3 \times 144 \times 6.75}{4} = 108 \times 6.75 = 729\)
\(\therefore r = \sqrt[3]{729} = 9\) cm.
(The initial water height 20 cm is not needed; only the rise matters.)