A tank is connected with both inlet pipes and outlet pipes. Individually, an inlet pipe can fill the tank in 7 hours and an outlet pipe can empty it in 5 hours. If all the pipes are kept open, it takes exactly 7 hours for a completely filled-in tank to empty. If the total number of pipes connected to the tank is 11, how many of these are inlet pipes?
Explanation:
Let there be x and y inlet and outlet pipes respectively.
∴ x + y = 11 … (i)
Assume that the capacity of the tank is 35 units.
So, inlet pipe fills 5 units and the outlet pipes empties 7 units of the tank in one hour.
The completely filled tank empties in 7 hours.
∴ 7y – 5x = 5 … (ii)
Solving the two equations, we get y = 5 and x = 6
Hence, option (d).
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