OG 13 DS Question 115

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by GMATGuruNY » Thu Nov 29, 2012 9:19 pm
Machines X and Y produced identical bottles at different constant rates. Machines X. operating alone of 4 hours, filled part of a production lot; then Machine Y, operating alone for 3 hours, filled the rest of this lot. How many hours would it have taken Machine X operating alone to fill the entire production lot?

1. Machine X produced 30 bottles per minute.
2. Machine X produced twice as many bottles in 4 hours as Machine Y produced in 3 hours.
Statement 1: X produced 30 bottles per minute.
Thus, the work produced by X in 240 minutes = r*t = 30*240.
No information about how much work was produced by Y.
INSUFFICIENT.

Statement 2: Machine X produced twice as many bottles in 4 hours as Machine Y produced in 3 hours.
Thus, for every bottle Y produced, X produced 2 bottles, implying that X produced 2 of every 3 bottles.
In other words, X produced 2/3 of the lot.
Since X took 4 hours to produce 2/3 of the lot, X would need 2 more hours to produce the remaining 1/3 of the lot, for a total of 6 hours.
SUFFICIENT.

The correct answer is B.
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by mcdesty » Fri Nov 30, 2012 10:41 am
Machine Rate Time(hrs) Work
X a/4 4 a
Y (x-a)/4 3 x-a
Total X

How long will X take alone? X /(a/4) = 4X/a

Translation..What is 4x/a
(1) a/4 = 0.5...Not information about X so insuff.
(2) a = 2(x-a)
a = (2/3)x
(4x)/(2/3x) = 6 ..Suff...
The method above is superior to mine...Pay more attention to the method above!!!