Exams › IBPS PO › Quantitative Aptitude

Three pipes A, B, and C are opened to fill a tank. Working alone, A, B, and C can fill the tank in 12 minutes, 15 minutes, and 20 minutes respectively. Another pipe D, which is an outlet pipe, can empty the fully filled tank in 30 minutes when working alone. What is the total time taken to fill the tank if all the pipes are opened simultaneously?

1. 3 minutes
2. 12 minutes
3. 6 minutes
4. 8 minutes

Correct answer: 6 minutes

Solution

A, B, and C fill at rates of $1/12$, $1/15$, and $1/20$ tank per minute. D empties at $1/30$ tank per minute, so the net rate is $1/12 + 1/15 + 1/20 - 1/30 = 1/6$ tank per minute. Hence, the tank is filled in 6 minutes.

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