Staphyk wrote:
Again, In a manufacturing plant, it takes 36 machines 4 hours of continuous work to fill 8 standard orders. At this rate, how many hours of continuous work by 72 machines are required to fill 12 standard orders?
This how I solved it
36machines——8orders——4hrs
72machines——12orders—— Xhrs
Now,Xhrs=4*(72/36)*(12/8) =12hrs
But was wrong
multiplied by 72/36 since machine increased so fraction (>1) same applies to the orders, Where did my logic go wrong.
Also,when is it appropriate to use the chain rule W1/M*T= W2/M*T
Thank you
Sent from my iPhone using
GMAT Club Forum mobile appYou need to find the number of hours required.
When the number of machines go up from 36 to 72, considering everything else constant, will you need more hours or fewer hours? Since the number of machines is more now, you will need less time. More machines will work simultaneously so the work will get completed faster. So you need to multiply 4 by (36/72), the fraction less than 1.
As for orders, from 8 they have gone up to 12 i.e. the work needed to be done has increased. When work to be done increases, keeping everything else constant, will you need more hours or fewer? Since more work has to be done, you need more hours. So you multiply by 12/8, the fraction greater than 1.
4 * (36/72) * (12/8) = 3 hrs
Answer (A)