SOLUTION: It takes a professional 7 hours to repair a roof. Working together, you and the professional can get the job done in 4 hours. How long would it take you to repair the roof working

Algebra ->  Rate-of-work-word-problems -> SOLUTION: It takes a professional 7 hours to repair a roof. Working together, you and the professional can get the job done in 4 hours. How long would it take you to repair the roof working       Log On


   

Question 491203: It takes a professional 7 hours to repair a roof. Working together, you and the professional can get the job done in 4 hours. How long would it take you to repair the roof working alone?
Found 2 solutions by stanbon, scott8148:
Answer by stanbon(75887) About Me  (Show Source):
You can put this solution on YOUR website!
It takes a professional 7 hours to repair a roof. Working together, you and the professional can get the job done in 4 hours. How long would it take you to repair the roof working alone?
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Professional rate: 1/7 job/hr
Together rate: 1/4 job/hr
Your rate: 1/x job/hr
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Equation:
rate + rate = together rate
1/7 + 1/x = 1/4
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Multiply thru by 28x
4x + 28 = 7x
3x = 28
x = 9 1/3 hrs = 9 hrs 20 min. (time for you to do the job alone)
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Cheers,
Stan H.

Answer by scott8148(6628) About Me  (Show Source):
You can put this solution on YOUR website!
in 4 hr, the professional does 4/7 of the roof ___ so you do 3/7

you want to know hours per roof so divide 4 by 3/7

and get 28/3 or 9 1/3 hr