A tap can fill a tank in 6 hours. After 4 hours it was found that only 60% of the tank is full due to a leakage at the bottom which was then immediately repaired. In how much time will the tank be completely filled?

Without any leakage, the tap fills the tank at a rate of:
Efficiency of tap=
6 hours
100%
​
=
3
50
​
% per hour
In 4 hours, without any leakage, the tank should have been filled by:

4×
3
50
​
%=
3
200
​
%=66.67%
However, due to leakage, only 60% is filled after 4 hours.
The remaining part of the tank to be filled is:

Remaining capacity=100%−60%=40%
At this point (after 4 hours), the leakage is completely repaired, so only the tap will operate at its original efficiency of
3
50
​
% per hour.

Time required to fill the remaining 40%=
Efficiency of tap
Remaining capacity
​

Time=
3
50
​

40
​
=40×
50
3
​
=
5
12
​
 hours=2.4 hours
Converting 2.4 hours into hours and minutes:

2 hours+0.4×60 minutes=2 hours 24 minutes
Total time from the start=4 hours+2 hours 24 minutes=6 hours 24 minutes