Rate Problem- GMATPrep 1

[Mjkourtis]

6 machines, working at the same rate, complete a job in 12 days. How many additional machines can complete the job in 8 days?
A. 2
B. 3
C. 4
D. 6
E. 8

[Brent@GMATPrepNow]

6 machines, working at the same rate, complete a job in 12 days. How many additional machines can complete the job in 8 days?
A. 2
B. 3
C. 4
D. 6
E. 8

If 6 machines take 12 days to complete the job, then we can say that the job takes 72 "machine days" to complete the job (6x12=72)

To complete the job in 8 days would require 9 machines (72 machine days divided by 8)

So, we need an additional 3 machines.

Answer = B

Cheers,
Brent