Exams › IBPS PO › Quantitative Aptitude

Two pipes A and B can fill a cistern in 37 minutes and 45 minutes respectively. Both pipes are opened. The cistern will be filled in half an hour if pipe B is turned off after:

1. 5 min.
2. 9 min.
3. 10 min.
4. 15 min.

Correct answer: 9 min.

Solution

Pipe A fills \(1/37\) cistern per minute and pipe B fills \(1/45\) cistern per minute. If B is turned off after \(x\) minutes, then \(x\left(\frac{1}{37}+\frac{1}{45}\right)+(30-x)\frac{1}{37}=1\). Solving gives \(x=9\) minutes.

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