Question 367596: Dal and Kim can assemble a swing set in 1 1/2 hr. Working alone, it takes Kim 4 hr longer than Dal to assemble the swing set. How long would it take Dal, working alone, to assemble the swing set? I do not have a clue how to set this up Please help!!!
Answer by mananth(16946)   (Show Source):
You can put this solution on YOUR website! Dal and Kim can assemble a swing set in 1 1/2 hr. Working alone, it takes Kim 4 hr longer than Dal to assemble the swing set. How long would it take Dal, working alone, to assemble the swing set?
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let Dal assemble in x hours
so he does 1/x of the job in 1 hour
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kim takes (x+4) hours
so he does 1/(x+4) of the job in 1 hour.
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Together they assemble in 3/2 hours
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1/x + 1/(x+4) = 3/2
(x+4+x)/x(x+4)= 3/2
2x+4 /x(x+4)= 3/2
2(2x+4)=3x(x+4)
4x+8 = 3x^2+12x
3x^2-4x+12x-8 =0
3x^2+8x-8=0
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find the roots by quadratic equation
discriminant = 160
x1= (-8+sqrt(160))/6
0.77 hours
Dal takes 0.77 hours to complete the job alone
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m.ananth@hotmail.ca
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