Q. Two pipes A and B can fill a tank in 20 minutes and 30 minutes respectively. If both pipes are opened together, the time taken to fill the tank is:
Answer: 12 minutes
Notes: Part of the tank filled by both pipes in one minute = $latex \frac{1}{20}+\frac{1}{30}&s=1$ Required time = $latex \frac{1}{\frac{1}{20}+\frac{1}{30}}=\frac{20\times 30}{50}=\frac{60}{5}&s=2$ ∴ Required time = 12 Minutes Hence option [D] is the right answer.

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