Posted by Lueshelle on Wednesday, April 25, 2012 at 10:33am.
Dal takes d
Kim takes k
Dal&Kim take b (for both)
1/b = 1/d + 1/k
1/(3/2) = 1/d + 1/(d+4)
2/3 = 1/d + 1/(d+4)
multiply through by 3d(d+4) to get
2d(d+4) = 3(d+4) + 3d
2d^2 + 8d = 3d + 12 + 3d
2d^2 + 2d - 12 = 0
d^2 + d - 6 = 0
(d+3)(d-2) = 0
d = -3 or 2
must have positive time, so d=2
That is, Dal takes 2 hours by himself
check:
1/2 + 1/6 = 2/3 = 1/(3/2)
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