A water tank in a village is normally filled in 8 hours but takes 2 hours longer to fill because of a leak in its bottom. If the tank is full, in how many hrs will the leak empty it ?

The time taken by the leak to empty the tank =  $\frac{1}{8} - \frac{1}{10} = \frac{5 - 4}{40} = \frac{1}{40}$

Therefore, the leak empties the tank in 40 hours.