The leak will make it empty in:
Answer: (3) 40 hours
A cistern is normally filled = 8 hours
Therefore, a cistern can fill in an hour = 1/8
But takes two hours to fill because of a leak in its bottom.
Then, time taken by a cistern to fill = 10 hours
Therefore, a cistern can fill in a an four = 1/10
So, The cistern is empty in an hour by leak = 1/8 – 1/10
= (5 – 4)/40
Thus, the leak will take it empty = 40 hours.
Hence, the correct answer is option (3) 40 hours.