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a water tank has an inlet pipe and a drain pipe. a full tank can be emptied
in 30 minutes if the drain is opened and an empty tank can be filled in 45 min.
with the inlet pipe opened. if both pipes are accidentally opened when the
tank is full, then how long will it take to empty the tank?
Let t = time required to empty the tank with both valves open
Let the empty tank = 1
In this case emptying is +, and filling is -
Multiply equation by 90
3t - 2t = 90
t = 90 min to empty with both valves open
90/30 - 90/45
3 - 2 = 1