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shivshankar054: Junior | Next Rank: 30 Posts; Posts: 12; Joined: Mon Dec 03, 2012 10:02 am

by shivshankar054 » Sat Apr 20, 2013 8:27 am

Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days?

A.2
B.3
C.4
D.6
E.9

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Source: Beat The GMAT — Problem Solving | Sat Apr 20, 2013 8:27 am

neha24: Senior | Next Rank: 100 Posts; Posts: 72; Joined: Fri Mar 01, 2013 8:45 amFollowed by: 4 members; Thanked: 12 times

by neha24 » Sat Apr 20, 2013 8:37 am

additional machine wud be 4 hence C
12x8=6x total new no of machines
----> total new number of machine wud be =16
so extra wud be 4

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Anju@Gurome: GMAT Instructor; Posts: 511; Joined: Wed Aug 11, 2010 9:47 amFollowed by: 86 members; Location: Delhi, India; Thanked: 344 times

by Anju@Gurome » Sat Apr 20, 2013 10:26 am

shivshankar054 wrote:Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days?

12 machines complete the shipment in 8 days.
So, we need 12*8 machine-days to complete the shipment.

Now, the shipment need to be completed in (8 - 2) = 6 days.
Hence, 12*8/6 = 8*2 = 16 machines required.
Therefore, (16 - 12) = 4 more machines are required.

The correct answer is C.

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GMATGuruNY: GMAT Instructor; Posts: 15539; Joined: Tue May 25, 2010 12:04 pmFollowed by: 1906 members; Location: New York, NY; Thanked: 13060 times; GMAT Score:790

by GMATGuruNY » Sat Apr 20, 2013 1:10 pm

shivshankar054 wrote:Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days?

A.2
B.3
C.4
D.6
E.9

The shipment is to be completed in 6 days instead of 8.
6/8 = 3/4.
Time and rate are RECIPROCALS: to complete the shipment in 3/4 the time, the work must be produced at 4/3 the rate.
Thus, the number of machines must increase by 1/3:
(1/3)12 = 4.

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Jeff@TargetTestPrep: GMAT Instructor; Posts: 1462; Joined: Thu Apr 09, 2015 9:34 amFollowed by: 22 members; Location: New York, NY; Thanked: 39 times

by Jeff@TargetTestPrep » Mon Dec 18, 2017 11:48 am

shivshankar054 wrote:Twelve identical machines, running continuously at the same constant rate, take 8 days to complete a shipment. How many additional machines, each running at the same constant rate, would be needed to reduce the time required to complete a shipment by two days?

A.2
B.3
C.4
D.6
E.9

We are given that 12 machines have a rate of 1/8. We want the shipment to be completed in 6 days, which means that the rate would be â…™. We need to determine the number of machines necessary to have that rate of 1/6. We can create the following proportion in which n = the new number of machines:

12/(1/8) = n(/1/6)

Multiplying the left side by 8/8 and the right side by 6/6, we get:

96 = 6n

16 = n

Thus, there would need to be 4 additional machines.

Answer: C

Jeffrey Miller
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