In a manufacturing plant, it takes 36 machines 4 hours of continuous

Hi,
apart from the method described away,
the choices give away the answer..

36 machines take 4 hours to fill 8 standard orders..
in next eq we are doubling the machines from 36 to 72, but the work is not doubling(only 1 1/2 times), so naturally time taken will be less than 4..
only A left

72 machines is twice 36. So in 4 hours 72 machines would fill 2 x 8 = 16 orders.

We want only 12 orders = 3/4 x 16. So we need only 3/4 x 4 = 3 hours.

Answer: A

The rate of 36 machines is 8/4 = 2 orders per hour. So the rate of 72 machines is 2 x 2 = 4 orders per hour.

Thus, it will take 72 machines 12/4 = 3 hours to fill 12 standard orders.

Answer: A

For the method used below, check this post: https://www.gmatclub.com/forum/veritas-prep-resource-links-no-longer-available-399979.html#/2015/1 ... made-easy/

You 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)

36*4/8= 18 hrs per order
so 18=72*hrs/12
hrs= 18*12/72 = 3 hrs IMO A