One of the two inlet pipes works twiceas efficiently as the other. The two, working
alongside a drain pipe that can empty a cistern all by itself in 8 hours, can fill the empty cistern in 8 hours. How many hours will the less efficient inlet pipe taketo fill the empty cistern by itself?

Efficiency is inversely proportional to time.

The one who is more efficient will take less time to complete work and the one is less efficient will take more time to complete work.

We are given that One of the two inlet pipes works twice as efficiently as the other.

So, the one of the two inlet pipes will take double time to complete its work.

Now we are given that empty cistern is less efficient .So, empty inlet will take double the time to complete work.

Now we are given that The two, working alongside a drain pipe that can empty a cistern all by itself in 8 hours, can fill the empty cistern in 8 hours.

So, twice of 8 hours = 16 hours will the less efficient inlet pipe take to fill the empty cistern by itself.

Thus 16 hours will the less efficient inlet pipe take to fill the empty cistern by itself