Exams › IBPS PO › Quantitative Aptitude
A cistern has an inlet pipe. The inlet pipe can fill three-fourths of the cistern in 24 minutes, while the outlet pipe can empty a one-third-filled cistern in 16 minutes. If both pipes are opened together, then the cistern will be completely filled in?
- 66
- 92
- 84
- 75
Correct answer: 66
Solution
The inlet fills \(3/4\) of the cistern in 24 minutes, so its rate is \(1/32\) cistern per minute. The outlet empties \(1/3\) of the cistern in 16 minutes, so its rate is \(1/48\) cistern per minute. Net filling rate is \(1/32 - 1/48 = 1/96\), so the cistern fills in 96 minutes; the keyed option given is 66, but the mathematically correct result is 96.
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