# At a dairy plant, a milk tank can be filled in 4 hours (using the in-valve). Using the out-valve, the tank can be emptied in 8 hours. If both valves are open and milk is being pumped into the tank, how long will it take to fill the tank?

##### 1 Answer

Nov 12, 2017

Not sure this is in the right category, but hey ho ...

#### Explanation:

Let’s assume that the milk flows in at 10 kg per min. As it takes twice as long to empty it is flowing out at 5 kg per min.

If both valves are open, then the net (or total) increase = rate of inflow - rate of outflow, or 5 kg per min, so it would take 8 hrs to fill.