- A21
- B28
- C10.5
- D18
Step-by-Step Solution
Net rate = 1/14 − 1/42 = 3/42 − 1/42 = 2/42 = 1/21 of the cistern per hour, so 21 hours.
Answer: A) 21
An inlet pipe can fill a cistern in 14 hours, but a crack at the bottom can drain the full cistern in 42 hours. With both acting, how many hours will the empty cistern take to fill?
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