  Question

It takes pump (A) $$4$$ hours to empty a swimming pool. It takes pump (B) $$6$$ hours to empty the same swimming pool. If the two pumps are started together, at what time will the two pumps have emptied $$50$$% of the water in the swimming pool?

A
1 hour 12 minutes  B
1 hour 20 minutes  C
2 hour 30 minutes  D
3 hours  E
5 hours  Solution

The correct option is D $$1\ hour\ 12\ minutes$$Work efficiency of pump A in emptying pool = $$\dfrac{1}{4}$$ per hourWork efficiency of pump B in emptying pool = $$\dfrac{1}{6}$$ per hour$$\therefore$$ work done by A and B together = $$\dfrac{1}{4} + \dfrac{1}{6} = \dfrac{10}{24}$$per hourHence time taken to fill the tank  $$100$$% = $$\dfrac{24}{10}$$ hours$$\therefore$$ time taken to fill $$50$$% = $$\dfrac{12\times 50}{5\times100}$$  = $$1.2$$ hoursSince, $$1 hour = 60 minutes$$$$\therefore 1.2$$ hours= $$1.2\times 60 = 72$$ minutes$$72$$ minutes = $$(60 +12)$$ minutes = $$1 hour$$  $$12 minutes$$So, the answer is option AMathematics

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