SOLUTION: Joe can do a certain job in 21 minutes. Bob can do the same job in 28 minutes. How long will it take them to complete the job if they work together?
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Question 640439: Joe can do a certain job in 21 minutes. Bob can do the same job in 28 minutes. How long will it take them to complete the job if they work together?
Answer by solver91311(24713) (Show Source): You can put this solution on YOUR website!
If A can do a job in x time periods, then A can do 
of the job in 1 time period. Likewise, if B can do the same job in y time periods, then B can do 
of the job in 1 time period.
So, working together, they can do
of the job in 1 time period.
Therefore, they can do the whole job in:
time periods.
John
My calculator said it, I believe it, that settles it
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