Multiple choice

A and B fill a tank in 12 minutes and 16 minutes respectively and pipe C can fill it in 8 minutes. A and B start filling the tank and after 5 minutes C starts filling the tank. In how much time will the tank be filled?

  1. 5 minutes

  2. 4 minutes

  3. 6 minutes

  4. 8 minutes
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Combined rate of A and B = 1/12 + 1/16 = 7/48 per minute. In 5 minutes, they fill 5 × 7/48 = 35/48. Remaining = 13/48. With C added, combined rate = 1/12 + 1/16 + 1/8 = 13/48 per minute. Time for remaining = (13/48) / (13/48) = 1 minute. Total time = 6 minutes.

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