Question
An inlet can fill an empty tank in 6 hours whereas an
outlet pipe can empty it in 12 hours. If (N - 1) such outlet pipes having same efficiency and (N + 1) such inlet pipes having same efficiency are opened together, then the tank gets filled in 3 hours. How many inlet pipes are used?Solution
Let the capacity of the tank be 12 litres (LCM of 6 and 12). Efficiency of 1 inlet pipe = 12/6 = 2 units/hour Efficiency of 1 outlet pipe = 12/12 = 1 units/hour According to the question, 
Required number of inlet pipes used = N+1 = 1+1 = 2
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