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Knewton Blog - Rate problem

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Knewton Blog - Rate problem

by GmatKiss » Fri Oct 14, 2011 10:15 am
Running at their respective constant rates, machine X takes 2 days longer to produce w widgets than machine Y. At these rates, if the two machines together produce (5/4)w widgets in 3 days, how many days would it take machine X alone to produce 2w widgets?

A) 4 B) 6 C) 8 D) 10 E) 12

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by sl750 » Fri Oct 14, 2011 11:01 am
R(x) = w/2+d; R(y) = w/d

Combined rate = R(x)+R(y) = 5w/12 = w/2+d + w/d;

5d^2+10d =24d+24
5d^2-14d-24=0
5d(d-4)+6(d-4) = 0; d=-6/5 or d=4

R(x) = w/6; T= 2w/(w/6) = 12
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