SOLUTION: A pool can be filled with water by a large pipe within 6 hours. A smaller pipe will take 9 hours to fill the pool. How long will it take the pool if the two pipes operate together?

Question 821731: A pool can be filled with water by a large pipe within 6 hours. A smaller pipe will take 9 hours to fill the pool. How long will it take the pool if the two pipes operate together?
Answer by TimothyLamb(4379) (Show Source): You can put this solution on YOUR website!
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NOTE TO STUDENT:
rate = (one job) / (time required to do the job)
rate = job / time
r = j / t
for this problem, the job is to fill the pool
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individual pipe rates:
r = 1/6
r = 1/9
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the rates of both pipes filling the pool together:
r = 1/6 + 1/9
r = 9/(6*9) + 6/(6*9)
r = 9/54 + 6/54
r = 15/54
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time per job is 1/r:
1/r = 1/(15/54)
1/r = 54/15
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answer:
1/r = 3.6 hours to fill the pool
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