A tap fills a tank in 4 hours and a drain empties it in 6 hours. If both are open, how long to fill the empty tank?

A8 hours

B10 hours

C12 hours

D14 hours

Explanation

Net rate per hour = 1/4 – 1/6 = (3 – 2) / 12 = 1/12. Time required = 12 hours.

Exam Relevance

Topic: Age Problems, Time & Distance, Work
Subtopic: Pipes & Cisterns

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