Working alone at their respective constant rates, Machine A & Machine B can fill a certain order in 3 hrs and 6 hrs, respectively. If the 2 machines work simultaneously at their constant rates, how many hours does it take the 2 machines to fill ½ of that order ?
(A) 1
(B) 5/4
(C) 3/2
(D) 7/4
(E) 1/2
Answer (Posted on Dec 12th): A
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