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At 12:00 noon, a machine, operating at a fixed rate, starts

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by swerve » Tue Jun 05, 2018 5:43 am

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At 12:00 noon, a machine, operating at a fixed rate, starts processing a large set of identical items. At 1:45 p.m., the twenty-first item has just been processed, and 15 have not yet been processed. At what time will all 36 items be processed?

A. 2:25 pm
B. 3:00 pm
C. 3:27 pm
D. 4:13 pm
E. 5:15 pm

The OA is B.

It takes 1h and 45 minutes to complete 21 items.

1h45m=7/4h.

Rate=21/(7/4)=12items/hour. 36 items are ready in 3 hours from noon. Option B.

Has anyone another strategic approach to solve this PS question? Regards!
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Source: — Problem Solving |

by Scott@TargetTestPrep » Wed Jun 06, 2018 3:58 pm
swerve wrote:At 12:00 noon, a machine, operating at a fixed rate, starts processing a large set of identical items. At 1:45 p.m., the twenty-first item has just been processed, and 15 have not yet been processed. At what time will all 36 items be processed?

A. 2:25 pm
B. 3:00 pm
C. 3:27 pm
D. 4:13 pm
E. 5:15 pm
We see that the machine processes 21 items in 1¾ hours, or 105 minutes. Thus, the rate of the machine is:

105/21 = 5 minutes per item

At this rate, the machine will process 36 items in 36 x 5 = 180 minutes, or 3 hours. So it will finish at 3:00 p.m.

Answer: B

Scott Woodbury-Stewart
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