SOLUTION: Computer A can do a job in 4 hours. Computer B can do the same job in 2 hours. How long will it take them to complete the job working together?

Question 393524: Computer A can do a job in 4 hours. Computer B can do the same job in 2 hours. How long will it take them to complete the job working together?
Found 2 solutions by stanbon, Earlsdon:
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
Computer A can do a job in 4 hours. Computer B can do the same job in 2 hours. How long will it take them to complete the job working together?
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A rate = 1/4 job/hr
B rate = 1/2 job/hr
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Together rate: 1/x job/hr
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Equation:
rate + rate = together rate
1/4 + 1/2 = 1/x
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Multiply thru by 4x to get:
x + 2x = 4
3x = 4
x = 4/3 = 1hr and 20 min (time to do the job together)
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Cheers,
Stan H.
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Answer by Earlsdon(6294) (Show Source): You can put this solution on YOUR website!
1) Find the hourly rate of computer A.
2) Find the hourly rate of computer B.
3) Add these to get the hourly rate of both computers working together.
4) Invert this number to get the time to complete the job working together.
If A can do the job in 4 hours, then it can do of the job in 1 hour.
If B can do the job in 2 hours, then it can do of the job in 1 hour.
Together, they can do of the job in 1 hour.
So, together, they can do the whole job in hours, or 1 hour and 20 minutes.
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