SOLUTION: 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

Question 464388: 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?

Answer by nerdybill(7384) (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?
.
Let d = time it takes for Dal alone
then
d+4 = time it takes for Kim
.
1.5(1/d + 1/(d+4)) = 1
multiplying both sides by d(d+4):
1.5(d+4 + d) = d(d+4)
1.5(2d+4) = d^2+4d
3d+6 = d^2+4d
6 = d^2+d
0 = d^2+d-6
0 = (d+3)(d-2)
d = {-3, 2}
toss out the negative solution leaving:
d = 2 hours (Dal's time working alone)

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