arithmetic - a tanker could be filled in 9 hours takes one hour more to be filled owing to a leak in its bottom if the tanker is full in what time will the leak empty it - skillgun

Solution: Required time be x hours.
Formula: If a pipe can fill a tank in x hours and another pipe can empty the full tank in y hours, then on opening both the pipes, the net part filled in 1 hour = (1/x - 1/y) (where y > x).
Then, 1/9 - 1/x = 1/10
=> 1/x = 1/9-1/10
=> 1/x = 1/90.
.'. leak will be empty it in 90 hours.