Question

There is a leak in the cistern. when the cistern is thoroughly repaired, it would be filled in 3 1/2 hours. It now takes half an hour longer. If the cistern is full, how long will the leak take to empty the cistern?

Answer 1

Answer:

Let's assume the tank has 12 litres capacity. The pipe can fill in 3 hours therefore efficiency= 12/3=4. Now the leak caused the tank to be filled in 3 1/2 hrs.

Total capacity/efficiency of pipe-efficiency of leak=time taken

ie,12/4-x=7/2

X=(28-24)/7= 4/7 which is the efficiency of d leak.

So time take by the leak to empty the tank is:

12÷ 4/7 12*7/4= 7*3 = 21 hours