Question 1207781
A bathroom tub will fill in 15 minutes with both faucets open and the stopper in
place.<pre>There are 4 15-minute periods in an hour, so in an hour the faucets will
have poured out 4 tub-fulls of water.</pre>With both faucets closed and the stopper removed, the tub will empty in 20
minutes.<pre>There are 3 20-minute periods in an hour, so in an hour the unstopped hole will
have drained out 3 tub-fulls of water.</pre>How long will it take for the tub to fill if both faucets are open and the
stopper is removed?<pre>So in an hour, 4 tub-fulls of water will have been poured into the tub, and 3
tub-fulls of water will have drained out of the tub, so just enough water will
remain to fill up 4-3=1 tub-full.<pre>Answer: 1 hour.

Edwin</pre>