While working alone at their constant rates, computer X can process files in hours, and computer Y can process files in 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 files?
Answer Choices
Correct answer marked belowSee the full step-by-step explanation
You can see the correct answer above. Sign in for free to unlock the complete worked solution.
Track your performance and improve
Get detailed analytics, unlock full explanations, and move up difficulty tiers as you practice.
Unlock the full explanation
Create a free account to reveal the correct answer, see the step-by-step explanation, and start tracking your GMAT progress.
X does 60 files/hr and Y does 30 files/hr, so combined 90. 240/90 is easy to see as 8/3 hrs. Nice clean numbers, thanks!
Same here, the rates came out really friendly.
Wait, why isn't it just the average of 4 and 8? I keep wanting to say 6 hrs but that's a trap choice...
Because you're adding rates, not times. Working together is always faster than the slower machine alone.
Yeah, once I wrote it as files per hour it clicked.
Got 2 hrs 40 min. Converting 2/3 of an hour to minutes is the only spot I could mess up.
Same, I almost picked 2 hrs 20 min by rushing the conversion.
Is this really sub-505? Maybe it's the wording that trips people, but the arithmetic is pretty light.
I think the 6-hr trap is what gets people, otherwise it's straightforward.
What it tests
Your ability to combine individual work rates, usually by working with the fraction of a job completed per unit of time.
Common trap
Adding the times instead of the rates, or forgetting to take the reciprocal when combining rates.