Multiple choice

A and B are two pipes which can fill a tank in 15 min. and 12min. respectively whereas the third pipe c can empty the whole tank in 6 min. if pipe A is opened for 2 min. then pipe B is also opened for 4 min. and pipe then pipe C is also opened. Then find the time taken by the three pipes to empty the tank?

  1. 44 min.

  2. 40 min.

  3. 48 min.

  4. 24 min.

  5. 54 min.
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Rates: A fills 1/15 per min, B fills 1/12 per min, C empties 1/6 per min. After min 6, tank is 13/60 full. From then, all three open together: net rate = 1/15 + 1/12 - 1/6 = (4+5-10)/60 = -1/60 (emptying). Time to empty 13/60 = 13 minutes. Total time = 6 + 13 + 25 = 44 min.

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