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

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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) About Me  (Show Source):
You can put this solution on YOUR website!
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Since the first tube can fill the reservoir in  4  hours,  it fills  1%2F4  of the reservoir volume per hour.
Since the second tube can fill the reservoir in  6  hours,  it fills  1%2F6  of the reservoir volume per hour.
Working simultaneously,  two tubes fill  1%2F4+%2B+1%2F6 = 3%2F12+%2B+2%2F12 = %283%2B2%29%2F12 = 5%2F12  of the reservoir volume per hour.
Hence,  the reservoir will be filled in  12%2F5 = 22%2F5  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.