Question 824307: Together, John and mark can finish painting a house in 10 hours. Alone, John takes 4 hours longer than Mark to finish painting the same house. How long does Mark take to finish painting the house by himself? Give your answer correct to 2 decimal place.
Answer by stanbon(75887)   (Show Source):
You can put this solution on YOUR website! Together, John and mark can finish painting a house in 10 hours.
Alone, John takes 4 hours longer than Mark to finish painting the same house. How long does Mark take to finish painting the house by himself?
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Mark:: time = x hrs/job ; rate = 1/x job/hr
John:: time = x+4 hrs/job ; rate = 1/(x+4) job/hr
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Together:: time = 10 hrs/job ; rate = 1/10 job/hr
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Equation:
rate + rate = together rate
1/x + 1/(x+4) = 1/10
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10(x+4) + 10x = x(x+4)
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20x + 40 = x^2 + 4x
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x^2 - 16x - 40 = 0
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x = [16 +- sqrt(256-4*-40)]/2
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x = [16 +- sqrt(96)]/2
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x = [16 +- 4sqrt(6)]/2
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x = [8 +- 2sqrt(6)]
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Comment: Strange answer for this type of problem.
Did you post it correctly?
Cheers,
Stan H.
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