IMO D,
Given - Machines Y and Z work at their respective constant rates (assuming those as y and z per hour respecitively). If it takes machines Y and Z, working together, 12 hours to fill a production order of a certain size (assuming w).
Therefore, w = 12(y+z) ----- (Eq1)
To calculate, how many more hours does it take machine Y, working alone, to fill the order than it takes machine Z, working alone lets check the given statements,
1st - Machine Z, working alone, fills a production order of this size in twice the time than machine Y, working alone, does (assuming y worked for t hours)
w = z*2t = y*t
Therefore, y=2z
substituting this in equation 1 we will get,
12(y+z) = z*2t,
as y=2z,
12*3z = z*2t
t=18 hours,
t' time for machine Z to complete the same order = 2*t = 36Hours,
So, machine Y doesnt take more time than Z. Hence Sufficient.
2nd - Machines Y and Z, working together, fill a production order of this size in two-thirds the time that machine Y, working alone, does (again assuming same y worked for t hours)
from this the equation we can get,
(2t/3) * (y+z) = y*t
on further solving,
2(y+z) = 3y
y=2z.
This is same we got from statement 1. Hence Sufficient.
But, machine Y doesnt take more time than Z. and question ask us to calculate "how many more hours does it take machine Y, working alone, to fill the order than it takes machine Z, working alone?"
Is there anything i am missing? Experts please advice?