Q. A pipe can fill a tank in x hours and another can empty it in y hours. In how many hours they can together fill it (where y > x) :
Answer: $latex \frac{xy}{y-x}\ hours&s=1$
Notes: When both pipes are opened simultaneously, part of the tank filled in 1 hour $latex = \frac{1}{x}-\frac{1}{y}=\frac{y-x}{xy}&s=1$ ∴ Required time $latex = \frac{xy}{y-x}\ hours&s=1$ Hence option [C] is correct answer.

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