A tank is normally filled in 18 hours by a pipe, but it takes 6 hours more to fill the tank due to a leakage at its bottom. The leakage point can empty the tank when it is two-third full in ______ hours.

Let the filling pipe be A and the leak be B.
Time taken by pipe A alone to fill the tank = 18 hours.
Due to the leak, the net time taken to fill the tank = 18+6=24 hours.

Let the total capacity of the tank be the LCM of 18 and 24, which is 72 units.

Efficiency of filling pipe A=
18
72
​
=4 units/hour
Combined efficiency of A and leak B=
24
72
​
=3 units/hour
Therefore, the efficiency of leak B is:

Efficiency of B=3−4=−1 unit/hour (emptying)
The leakage point needs to empty
3
2
​
of the total capacity:

Work to be done=
3
2
​
×72=48 units
Time taken by leak B=
1
48
​
=48 hours.