Q. It would take one machine 4 hours to complete a production order and another machine 2 hours to complete the same order. If both machines work simultaneously at their respective constant rates, the time taken to complete the same order is_______________hours.
(A) 2/3
(B) 3/4
(C) 4/3
(D) 7/3
Ans: 4/3
Solution:
Machine X=4 hours
Machine Y=2 hours
In 1 hour X can work=1/4
In 1 hour Y can work=1/2
In 1 hour (X+Y) can work
=1/4+1/2=3/4
(X+Y) together=4/3 hours
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