While working alone at their constant rates computer X can process 240 file in 4 hours...

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GMAT Prep

While working alone at their constant rates computer X can process 240 files in 4 hours, and computer Y can process 240 files in 8 hours. If all files processed by these computers are the same size how long would it take the two computers working at the same time at their respective constant rates, to process a total of 240 files?

A. 2 hours
B. 2 hours 20 minutes
C. 2 hours 40 minutes
D. 6 hours
E. 6 hours 20 minutes

OA C

[Scott@TargetTestPrep]

GMAT Prep

While working alone at their constant rates computer X can process 240 files in 4 hours, and computer Y can process 240 files in 8 hours. If all files processed by these computers are the same size how long would it take the two computers working at the same time at their respective constant rates, to process a total of 240 files?

A. 2 hours
B. 2 hours 20 minutes
C. 2 hours 40 minutes
D. 6 hours
E. 6 hours 20 minutes

OA C

Solution:

The rate of computer X is 240/4 = 60 files in 1 hour and the rate of computer Y is 240/8 = 30 files in 1 hour, so the combined rate is 90 files in 1 hour. Thus, it takes 240/90 = 2 60/90 hours = 2 ⅔ hours = 2 hours and 40 minutes to complete 240 files when both computers work together.

Answer: C