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A tap having diameter 'd' empty a tank in 40 min. How long another tap having diameter '2d' take to empty the same tank?

5 min
20 min
10 min
80 min

Correct Answer: 20 min

Explanation:

Area of tap ∝ Work done by pipe.
When diameter is doubled, area will be four times. so, it will work four times faster.
Hence, required time taken to empty the tank = 40 x 1/4 = 10 min.

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