Q. A tap can fill a cistern in 8 hours and another tap can empty it in 16 hours. If both the taps are open, the time (in hours) taken to fill the tank will be:
Answer: 16 hours
Notes: Part of the cistern filled in 1 hour = 1$latex \div$8 Part of the cistern emptied in 1 hour = 1$latex \div$16 When both the taps are opened simultaneously, part of cistern fill in 1 hour = $latex \frac{1}{8}-\frac{1}{16}=\frac{2-1}{16}=\frac{1}{16}&s=1$ Hence, the cisatern wil be filled in 16 hours. So option [B] is the right answer.

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