Question
There are two inlet pipes 'P', 'Q' and one outlet pipe 'R'
in a tank. ‘P’ and ‘Q’ can fill the tank in 20 minutes and 10 minutes respectively. ‘R’ is 50% less efficient than ‘P’. If ‘P’ and ‘R’ are open together but after 10 minutes, ‘P’ is replaced with ‘Q’, find the total time required to fill the tank completely.Solution
Tank capacity = 20x units (LCM of 20 and 10).
P = x units/min, Q = 2x units/min, R = 0.5x units/min
First 10 mins: (x - 0.5x) × 10 = 5x units
Remaining = 20x - 5x = 15x units
Net rate = 2x - 0.5x = 1.5x
Time = 15x / 1.5x = 10 minutes
Total time = 10 + 10 = 20 minutes
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