# A water tank can be filled with two pipes, P and Q, in 20 minutes and

| A water tank can be filled with two pipes, P and Q, in 20 minutes and 25 minutes, respectively. Both pipes are opened together but due to some technical problem, the efficiency of pipes is decreased by 40% and 50%, respectively. After some time, the problem is resolved and the total time taken to fill the tank is 16 minutes now. How long did the problem persist?

A. 11 minutes

B. 10 minutes

C. 9 minutes

D. 13 minutes

### Right Answer is: A

#### SOLUTION

Let the total capacity of water tank = 100

Efficiency of Pipe ‘P’ = 5

Efficiency of Pipe ‘Q’ = 4

Net efficiency = 5+ 4 = 9

But due to some technical problem, the efficiency of pipes, P and Q, is decreased by 40% and 50%, respectively,

So, Efficiency of Pipe ‘P’ after the technical problem = 5 –

New Efficiency of Pipe ‘Q’ after the technical problem= 4-

Net efficiency after the technical problem = 3+2 = 5

Now let the problem persist for t minutes.

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A water tank can be filled with two pipes, P and Q, in 20 minutes and