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"...it takes machines Y and Z, working together, 12 hours to fill a production order..." = \(\frac{1}{y}+\frac{1}{z}=\frac{1}{12}\)

­(1) Machine Z, working alone, fills a production order of this size in twice the time than machine Y, working alone, does

From this one knows that \(z = 2y\). Plugging this back into the equation above:

\(\frac{1}{y}+\frac{1}{2y}=\frac{1}{12}\)

\(\frac{3y}{2y^2}=\frac{1}{12}\)

\(\frac{3}{2y}=\frac{1}{12}\)

\(2y = 36\) as we know that \(2y = z\) then \(z = 36\) and \(y = 18\)

\(36 - 18 = 18\) hours more.

SUFFICIENT


(2) Machines Y and Z, working together, fill a production order of this size in two-thirds the time that machine Y, working alone, does

Together Y and Z can complete an order in 12 hours, therefore 
\(\frac{2}{3}y = 12\)

\(y = 18\), plugging this back into \(\frac{1}{y}+\frac{1}{z}=\frac{1}{12}\) and solving for x.

\(\frac{1}{18}+\frac{1}{z}=\frac{1}{12}\)

\(\frac{1}{z}=\frac{1}{12}-\frac{1}{18}\)

\(\frac{1}{z}=\frac{3-2}{36}\)

\(z=36\)

\(36 - 18 = 18\) hours more.

SUFFICIENT                   


ANSWER D                                                       
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Answer D

1. Rz=a/2t, Ry= A/t
(a/2t+a/t)=a/12
You get t an 2t
So you can calculate --> 2t-t - sufficient

2. 2/3 ty = 12
so you get ty
then you can calculate tz
and you can get tz-tx - sufficient­
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