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Question 535923: If one pipe takes 9 days and the other pipe 15 how long will bout take to fill the pool up
Answer by oberobic(2304)   (Show Source):
You can put this solution on YOUR website! Set up problems like these as fractions of the work done by each resource per unit of time.
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Pipe 1 takes 9 days, so it does 1/9 of the job per day.
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Pipe 2 takes 15 days, so it does 1/15 of the job per day.
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Working together, how long does it take to do the job?
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(1/9 + 1/15)*x = 1 job
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(15+9)/(9*15)*x = 1
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24/135 * x = 1
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24*x = 135
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x = 135/24 = 45/8 = 5 5/8 = 5.625 days
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To check, determine how much each can do in that amount of time.
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1/9*45/8 = 45/72 = 5/8
1/15 * 45/8 = 3/8
5/8 + 3/8 = 1
Correct
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Working together will take 5 5/8 days.
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Done.
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