Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized for You

we will pick new questions that match your level based on your Timer History

Track Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

It appears that you are browsing the GMAT Club forum unregistered!

Signing up is free, quick, and confidential.
Join other 500,000 members and get the full benefits of GMAT Club

Registration gives you:

Tests

Take 11 tests and quizzes from GMAT Club and leading GMAT prep companies such as Manhattan GMAT,
Knewton, and others. All are free for GMAT Club members.

Applicant Stats

View detailed applicant stats such as GPA, GMAT score, work experience, location, application
status, and more

Books/Downloads

Download thousands of study notes,
question collections, GMAT Club’s
Grammar and Math books.
All are free!

Thank you for using the timer!
We noticed you are actually not timing your practice. Click the START button first next time you use the timer.
There are many benefits to timing your practice, including:

Six machines, each working at the same constant rate, togeth [#permalink]

Show Tags

27 Nov 2006, 03:04

1

This post received KUDOS

2

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

15% (low)

Question Stats:

75% (01:46) correct
25% (01:08) wrong based on 187 sessions

HideShow timer Statistics

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines each working at the same constant rate, will be needed to complete the job in 8 days?

Assume N machines are needed and each machine does M amount of work

Let R be the rate of working of each machine 6/R=1/12 hence, R=72 Let X be the total no of machines which can complete work in 8 days X/R=1/8 Put value of R=72 Solving X=9 Hence additional no of machines required =9-6=3 Hence B

jairus wrote:

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each woring at the same constant rate, will be needed to complete the job in 8 days?

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each woring at the same constant rate, will be needed to complete the job in 8 days?

A) 2

B) 3

C) 4

D) 6

E) 8

Work Rate = 1/Time taken

Work Rate for 6 machines = 1/12 Work Rate for 1 machine = 1/12*6 = 1/72

Wor Rate for X machines = x/72 = 1/8 --> x=9

Answ = 9-6=3

B _________________

Your attitude determines your altitude Smiling wins more friends than frowning

For work related problems, number of person days or machine days is always constant Let x be the number of machines that were used to complete the work in 8 days. So, 6*12 = 8*x x = 9 Number of machines to be added = 9-6 = 3

Here number of machines and days are inversely proportional. 6 machine can complete the work in 12 days, so in 1 day all together can complete 1/12 part of work. Now to complete 1/8 part of work, 6 -- 1/12 x -- 1/8 x =6/8*12 x=9 Number of machines to be added = 9-6 = 3

6 machines each working at the same constant rate together can complete a job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

I think I saw this one in the first PowerPrep Test:

This is a simple two equation problem:

let x = the number of additional machines needed to complete the job in 8 days let y = the rate for one machine to complete the job

This solution is much faster and doesn't require you to calculate the rate of each of the machines -

6 machines ---> 12 days ? machines ---> 8 days.

the trick is to consider proportions since all machines are running at constant rate. so the number of machines is inversely proportional to number of days taken to complete the job. More number of machines to finish in lesser number of days - plain logic.

Under such situations, the blind approach is to multiply 6 with 12 and divide by 8, gives total number of machines to finish in 8 days, additional machines would be to just subtract with original number of machines. 9 - 6 = 3.

If the proportion was straight and not inverse, we would have multiplied 6 with 8 and divided with 12, but in inverse proportions, same line elements are multiplied. _________________

18.Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

A) 2 B) 3 C) 4 D) 6 E) 8

Rate of one machine = 1 job / (12*6) days

let X = number of machines needed to complete the job in 8 days

18.Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days?

A) 2 B) 3 C) 4 D) 6 E) 8

Rate of one machine = 1 job / (12*6) days

let X = number of machines needed to complete the job in 8 days

got this question on gmatprep...i know its an easy question but dunno why today i jus wasnt able to come 2 eqtns>>

Q> 6 machines at the same constant rate can do a work in 12 days,if the work has to be done in 8 days, how many machines which work at the same constant rate, need to be added.???

Follow this formula, it will be always easy.. * Different number of machines (or men) , change the number of days(hours) , but the product of the number of machines and number of days remain the same

M1 * D1 = M2 * D2 M= number of machines D= number of days 6 * 12 = M2 * 8 M2 = 9, so 3 more

* another formula when amount of work is different from the original, will be useful in some problems. (M1 * D1) / W1 = (M2 * D2)/W2 W = amount of work

Re: Six Machines Working Together GMAT Prep [#permalink]

Show Tags

25 May 2014, 13:05

Hello from the GMAT Club BumpBot!

Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up - doing my job. I think you may find it valuable (esp those replies with Kudos).

Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email. _________________

Six machines, each working at the same constant rate, together can complete a certain job in 12 days. How many additional machines, each working at the same constant rate, will be needed to complete the job in 8 days? A. 2 B. 3 C. 4 D. 6 E. 8

Let \(x\) be the time needed for 1 machine to complete the job, so rate of one machine is \(\frac{1}{x}\) (rate is the reciprocal of time) --> rate of 6 machines would be \(\frac{6}{x}\).

As \(job=time*rate\) --> \(1=12*\frac{6}{x}\) --> \(x=72\) days needed for 1 machine to complete the job.

To complete the job in 8 days \(\frac{72}{8}=9\) machines are needed.

This is the kickoff for my 2016-2017 application season. After a summer of introspect and debate I have decided to relaunch my b-school application journey. Why would anyone want...

Check out this awesome article about Anderson on Poets Quants, http://poetsandquants.com/2015/01/02/uclas-anderson-school-morphs-into-a-friendly-tech-hub/ . Anderson is a great place! Sorry for the lack of updates recently. I...