Multiple choice

A tank is filled in 5 hours by pipes A, B and C. Pipe C is twice as fast as B and B is twice as fast as A. How much time will pipe A alone take to fill the tank?

  1. 35 hours

  2. 30 hours

  3. 12 hours

  4. 53 hours

  5. 55 hours
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A Correct answer
Explanation

Let the rate of A be x. Then B is 2x and C is 4x. Their combined rate is x + 2x + 4x = 7x. Since they fill the tank in 5 hours, the total work is 7x * 5 = 35x. Pipe A alone takes 35x / x = 35 hours.

AI explanation

By establishing the relative efficiency ratios, pipe C is twice as fast as B and B is twice as fast as A, making their capacities in the ratio of 1:2:4 for A, B, and C respectively. Since their combined capacity represents 7 units and they fill the tank in 5 hours, their combined hourly rate is 1/5 of the tank. Using the ratio, pipe A accounts for 1/7 of this total work, so the time taken by A alone is 7 multiplied by 5, which equals 35 hours.

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