posted by Sandy .
Tap A fills a tube with cold water in 6 minutes. Tap B fills a tube with hot water in 8 minutes. If water is flowing out from taps A and B at the same time, how long does it take to fill the tubes?
A's rate = 1/6
B's rate = 1/8
combined rate = 1/6 + 1/8 = 7/24
time to fill with combined rate = 1/(7/24) = 24/7 minutes