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An inlet fills a sump in 25 minutes and an outlet drains it in 50 minutes. Opened together on the empty sump, how long do they take to fill it?

Competition practicePipes & Cisterns

A75 min
B25 min
C50 min
D $16 \frac{2}{3}$ min

Step-by-Step Solution

Net

= \frac{1}{25} - \frac{1}{50} = \frac{1}{50}

per minute → 50 min

. (16 \frac{2}{3}

min wrongly adds the outlet's rate.)

Answer: C) 50 min

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