SOLUTION: John by himself can paint 4 rooms in 10 hrs. if he hires Mark to help, they can do the same job together in 6 hrs. if he lets Mark work alone, how long will it take for Mark to pai

Question 347351: John by himself can paint 4 rooms in 10 hrs. if he hires Mark to help, they can do the same job together in 6 hrs. if he lets Mark work alone, how long will it take for Mark to paint 4 rooms?
Answer by stanbon(75887) (Show Source): You can put this solution on YOUR website!
John by himself can paint 4 rooms in 10 hrs. if he hires Mark to help, they can do the same job together in 6 hrs. if he lets Mark work alone, how long will it take for Mark to paint 4 rooms?
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John DATA:
time = 10 hrs/job ; rate = 1/10 job/hr
-----------------------
Together DATA:
time = 6 hrs/job ; rate = 1/6 job/hr
-----------------------
Mark DATA:
time = x hrs/job ; rte = 1/x job/hr.
=======================================
Equation:
rate + rate = together rate
1/10 + 1/x = 1/6
Multiply thru by 30x to get:
3x + 30 = 5x
2x = 30
x = 15 hrs (time for Mark to do the job alone)
========================
Cheers,
Stan H.

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