Question 67

The inlet to a tank can fill it in 4 hours while the outlet to the tank can empty it in 5 hours Both the pipes were opened at 9 Am but after sometime the outlet was closed and it is observed that the tank was full at 5 PM. At what time was the outlet closed ?

Solution

Let the outlet be open for x hours.

Let there be 100 units of water in the tank.

So, the speed of inlet is 25 units per hour and speed of the outlet is - 20 units per hr.

Let them be open for x hours. So, the total tank filled is 25 x - 20x =5x

For 8 - x hours the inlet is open. So, units of water = (8-x)*25

But that sum = 100

5x + 200 - 25 x = 100

20 x = 100

So, x = 5 hours. ie till 2 PM

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