A cistern has two pipes. Pipe A fills it in 8 hours and Pipe B empties it in 12 hours. If both are opened together, how long to fill the cistern?

A16 hours

B20 hours

C24 hours

D30 hours

Explanation

Net rate = 1/8 – 1/12 = (3 – 2)/24 = 1/24 per hour. Time required = 24 hours.

Exam Relevance

Topic: Work and Time
Subtopic: Pipes and Cisterns

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