Q. If pipes, A and B, together can fill a tank in 20 minutes and A alone can fill in 30 minutes. Then pipe B alone can fill the tank in :
Answer: 60 minutes
Notes: Because according to the question, part of the tank filled by pipe B in $latex 1\ minute\ = \frac{1}{20}-\frac{1}{30}= \frac{3-2}{60}= \frac{1}{60}&s=1$ Hence pipe B alone can fill the tank in 60 minutes, and option [B] is correct answer.

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