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:

A company has two types of machines,type R and type S. [#permalink]

Show Tags

17 Jan 2010, 13:01

4

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

95% (hard)

Question Stats:

30% (02:39) correct
70% (02:00) wrong based on 192 sessions

HideShow timer Statistics

A company has two types of machines, type R and type S. Operating at a constant rate a machine of R does a certain job in 36 hours and a machine of type S does the job in 18 hours. If the company used the same number of each type of machine to do job in 12 hours,how many machine R were used?

A company has two types of machines,type R and type S.Operating at a constant rate a machine of R does a certain job in 36 hours and a machine of type S does the job in 18 hours .If the company used the same number of each type of machine to do job in 12 hours,how many machine R were used? A.3 B.4 C.6 D.9 E.12 Answer:C But how?

Rate of A - \(\frac{1}{36}\) job/hour, rate of x machines of A - \(\frac{1}{36}x\) job/hour; Rate of B - \(\frac{1}{18}\) job/hour, rate of x machines of B - \(\frac{1}{18}x\) job/hour, (same number of each type);

Remember that we can sum the rates, hence combined rate of A and B is \(\frac{1}{36}x+\frac{1}{18}x=\frac{3}{36}x=\frac{1}{12}x\) job/hour.

We are told that together equal number (x in our case) of machines A and B can do the job (1 job) in 12 hours --> \(Time*Rate=12*\frac{1}{12}x=1=Job\) --> \(x=1\).

There is no correct answer listed. There must be a typo in the stem or in the answer choices.

As you stated that the correct answer is C (6), I'd suggest that there should be 2 hours instead of 12. If so, then the last step: \(Time*Rate=2*\frac{1}{12}x=1=Job\) --> \(x=6\).
_________________

A company has two type of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hours and machine of type S does the same job in 18 hours. If the company used the same number of each type of machine to do the job in 2 hours, how many machines of type R were used.

3 4 6 9 12

this is confusing me " company used the same number of each type of machine to do the job in 2 hours"

@bunuel, not sure whether I am right on this, but could I go for the following solution as well (assuming that we are looking for a combined time of 2 hours):

How can you assume x=2? If same no. of machines S and R taken together, then the task will be done in exactly 12 hours requiring 1 machine of each type. As Bunuel mentioned, this may be a typo error for 12 instead of 2.
_________________

Want to improve your CR: http://gmatclub.com/forum/cr-methods-an-approach-to-find-the-best-answers-93146.html Tricky Quant problems: http://gmatclub.com/forum/50-tricky-questions-92834.html Important Grammer Fundamentals: http://gmatclub.com/forum/key-fundamentals-of-grammer-our-crucial-learnings-on-sc-93659.html

yes there is a typo in the question, I got the same ques on my GMAT PREP last week, and the questions goes as:

A company has two types of machines,type R and type S.Operating at a constant rate a machine of R does a certain job in 36 hours and a machine of type S does the job in 18 hours .If the company used the same number of each type of machine to do job in 2 hours,how many machine R were used?

So for a job to be done in 2 hours R = 1/2

R_a(Rate of Machine R) = 1/36 R_s(Rate of Machine S) = 1/18 Lets say x machines are used to attain the desired rate, thus x/36+x/18 = 1/2 (Desired R =1/2 i.e. to complete the job in 2 hours) (x+2x)/36 = 1/2 3x/36 = 1/2 x = 6.

Re: A company has two types of machines,type R and type S. [#permalink]

Show Tags

26 Jan 2014, 14:02

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.
_________________

Hey, guys, So, I’ve decided to run a contest in hopes of getting the word about the site out to as many applicants as possible this application season...

Whether you’re an entrepreneur, aspiring business leader, or you just think that you may want to learn more about business, the thought of getting your Masters in Business Administration...

Term 1 has begun. If you're confused, wondering what my post on the last 2 official weeks was, that was pre-term. What that means is that the school...