A tall cylindrical container with circular base of radius 18 cm contains a good quantity of water. Metal balls each of radius 0.9 cm are immersed in it. How many balls are required to raise the water level by 3 cm?

  1. A. 100
  2. B. 500
  3. C. 1000
  4. D. 1500

Correct Answer: C. 1000

Explanation

Volume of water displaced = \pi \times 18^2 \times 3. Volume of one spherical ball = \frac{4}{3} \pi (0.9)^3. Number of balls = \frac{\pi \times 324 \times 3}{\frac{4}{3} \pi \times 0.729} = \frac{972}{0.972} = 1000.

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