With the stopper in place and the faucet running, a bathtub can be filled in 16 minutes. With the faucet off and the stopper removed, the tub will empty in 20 minutes. If the faucet is running and the stopper is not in place, how long will it take to fill the tub?

Solution:

The time it will take to fill the tub

1/x = 1/16+1/20

x = 8.89

So time it will take to fill the tub is 8.89 minutes