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Two pipes running together fill a tank in 6 minutes. If one pipe takes 5 minutes longer than the other, how long does the faster pipe take alone?

Competition practicePipes & Cisterns

A15 min
B12 min
C8 min
D10 min

Step-by-Step Solution

\frac{1}{x} + \frac{1}{x + 5} = \frac{1}{6} \Rightarrow x^{2} - 7 x - 30 = 0 \Rightarrow x = 10

. Check:

\frac{1}{10} + \frac{1}{15} = \frac{1}{6}

. (15 min is the slower pipe.)

Answer: D) 10 min

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