SOLUTION: I need help with this problem: Two pipes are used to fill a large tank. When used alone, pipes A and B take 4 hours and 6 hours, respectively, to fill the tank. How many hours wo

Question 987142: I need help with this problem:
Two pipes are used to fill a large tank. When used alone, pipes A and B take 4 hours and 6 hours, respectively, to fill the tank. How many hours would it take to fill the tank if the two pipes were used simultaneously.
Answer by ikleyn(52781)   (Show Source): You can put this solution on YOUR website!
.
Since the first tube can fill the reservoir in 4 hours, it fills    of the reservoir volume per hour.
Since the second tube can fill the reservoir in 6 hours, it fills    of the reservoir volume per hour.
Working simultaneously, two tubes fill = = = of the reservoir volume per hour.
Hence, the reservoir will be filled in = hours, or 2 hours and 24 minutes, if both tubes work simultaneously.

Answer. It will take 2 hours and 24 minutes to fill the reservoir, if two tubes work simultaneously.

It is a typical problem on joint work. For more of such problems and their solutions see my lesson Using fractions to solve word problems on joint work in this site.

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