Question 574909
If 5 girls and 2 boys work together they can paint a house in a day. Three girls and 6 boys working together can also paint the house in a day. How long would it take one boy to paint the house by himself?
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Let girl rate = g
Let boy's rate = b
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Equations: 
5g + 2b = 1
3g + 6b = 1
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Multiply  thru 1st equation by 3
Multiply thru 2nd equation by 5
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15g + 6b = 3
15g + 30b = 5
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Subtract and solve for "b":
24b = 2
b = 1/12 job/day
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Time for a boy to do the job alone 12 days/job
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Cheers,
Stan H.