Name: Jeffrey

Who is asking: Other
Level: Secondary

Question:
A bathtub, with two taps, can be filled in 20 minutes using only the cold water tap. It can be filled in 30 minutes using only the hot water tap. The flow of each tap is not changed when both taps are turned on. It takes 24 minutes to drain the full tub. Starting with an empty tub and the drain plug in place, the cold water turned on. Five minutes later the hot water is also turned on, and five minutes after that the drain plug is removed. How many additional minutes, after the plug is removed, would it take to fill the tub?

Hi Jeffrey,

If you think of a "tub" as a unit of volume then you can write each of the flow rates in tubs/min for example the cold water flows at 1/20 tubs/min. Rates can then be added or subtracted depending on which taps are on or off and whether the drian is open or closed.

Cheers
Harley