# A water tank can be filled by an inlet pipe in 8 hours. It takes twice that long for the outlet pipe to empty the tank. How long will it take to fill the tank if both pipes are open?

Aug 31, 2017

If both pipes are open, it fills the tank in $16$ hours .

#### Explanation:

Inlet pipe fills water tank in $8$ hours.

Outlet pipe empties the tank in $8 \times 2 = 16$ hours,

therefore, outlet pipe empties half the tank in $8$ hours, while inlet pipe has filled the tank in same $8$ hours.

therefore, if both pipes are open in $8$ hours it fills only half the tank.

Hence, if both pipes are open, it fills the tank in $8 \times 2 = 16$ hours .