SOLUTION: John can do a job in 4 hours and Mark can do the same job in 2 hours. If they work together, how long will the job take?

Question 801832: John can do a job in 4 hours and Mark can do the same job in 2 hours. If they work together, how long will the job take?
Answer by Cromlix(4381) (Show Source): You can put this solution on YOUR website!
John can do a job in 4 hours
Mark can do the same job in 2 hours
How long will the job take if they
work together?
John's rate = 1/4 job/hr
Mark's rate = 1/2 job/hr
Together rate = 1/x
1/4 + 1/2 = 1/x
Common denominator = 4x
x + 2x = 4
3x = 4
x = 4/3 or 1 1/3 hours
1/3 of an hour = 20 minutes
1 1/3 = 1 hour 20 minutes.
Hope this helps.
:-)
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