The question is from Pipes and Cisterns: Fill pipes and Drain Pipes. Again a question on possible values. How many fill and drain pipes required to fill the tank in 'x' hours? Find a complete "Null System". Work on the question after that.
Question 5: A fill pipe can fill a tank in 20 hours, a drain pipe can drain a tank in 30 hours. If a system of n pipes (fill pipes and drain pipes put together) can fill the tank in exactly 5 hours, which of the following are possible values of n (More than one option could be correct)?
3 fill pipes cancel out 2 drain pipes. Plus, you need an additional 4 fill pipes fill the tank in 5 hours. so the answer has to be 5k + 4.
Both 54 and 29 are possible.
The question is "which of the following are possible values of n?"
Choice D is the correct answer.
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