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Question 956010: Dave can do the job in 30 days. Giles can do it in 40 days, and Jon can do it 60 days. How long will it take them if they work together?
Answer by ptaylor(2198)   (Show Source):
You can put this solution on YOUR website! Dave can do the job in 30 days. Giles can do it in 40 days, and Jon can do it 60 days. How long will it take them if they work together?
Let x=amount of time needed for the three to do the job when they work together
Then they work at the rate of 1/x of the job per day
Dave works at he rate of 1/30 of the job per day
Giles works at the rate of 1/40 of the job per day
Jon works at the rate of 1/60 of the job per day
Sooooo
1/30 + 1/40 + 1/60= 1/x multiply each term by 120x
4x+3x+2x=120
9x=120
x=13 1/3 days---time needed if they work together
CK
In 13 1/3=40/3 days, Dave completes (40/3)(1/30)=4/9 of the job
In 40/3 days, Giles completes (40/3)(1/40)=1/3=3/9 of the job
In 40/3 days, Jon completes (40/3)(1/60) =2/9 of the job
4/9 + 3/9 +2/9=1 job completed:)
Hope this helps----ptaylor
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