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 350,000 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]
02 Apr 2012, 12:55

8

This post was BOOKMARKED

00:00

A

B

C

D

E

Difficulty:

25% (medium)

Question Stats:

70% (02:06) correct
30% (01:13) wrong based on 344 sessions

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a 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?

A company has two types of machines, type R and type S [#permalink]
02 Apr 2012, 16:58

5

This post received KUDOS

Expert's post

4

This post was BOOKMARKED

enigma123 wrote:

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a 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?

A. 3 B. 4 C. 6 D. 9 E. 12

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 2 hours --> \(Time*Rate=2*\frac{1}{12}x=1=Job\) --> \(x=6\).

Re: A company has two types of machines, type R and type S [#permalink]
03 Apr 2012, 05:49

enigma123 wrote:

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a 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?

A. 3 B. 4 C. 6 D. 9 E. 12

Take total work as 360

R: work : 360 time: 36hrs rate: 10(calculaed)

S: Work:360 time 18hrs rate: 20( calculated)

together

given work:360 time2 hrs calculated: 180 rate: 180/(10+20) = 180/30 = 6 each _________________

Regards, Harsha

Note: Give me kudos if my approach is right , else help me understand where i am missing.. I want to bell the GMAT Cat

A company has two types of machines, type R and type S [#permalink]
15 Aug 2012, 10:16

1

This post received KUDOS

above720 wrote:

Here is a work problem from GMATPrep, Practice Test 1:

A company has two types 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 a machine of type S does the same in 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?

a) 3 b) 4 c) 6 d) 9 e) 12

Machine R does a job in 36 Hours. Machine S in 18 Hours. Together, the machines R & S can finish the job in \(\frac{(36*18)}{(36+18)}= 12 Hours\) In other words, 1 machine of R + 1 machine of S can finish the job together in = 12 Hours

So, to finish the job in 2 Hours, company needs 6 machines of each type - Option C

Re: A company has two types of machines, type R and type S [#permalink]
25 Feb 2013, 13:29

I am not sure I understand your question correctly. The number of machines is not equal to the time. Instead, the number of machines has to be replied with the time taken by each machine to get the total time required to complete the job.

Hope this helps but in case it doesn't, could you please state your question more elaborately?

fozzzy wrote:

So the number of macines in this question is just the time in this particular question?

Re: A company has two types of machines, type R and type S [#permalink]
04 Mar 2013, 02:45

arnabghosh wrote:

above720 wrote:

Here is a work problem from GMATPrep, Practice Test 1:

A company has two types 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 a machine of type S does the same in 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?

a) 3 b) 4 c) 6 d) 9 e) 12

Machine R does a job in 36 Hours. Machine S in 18 Hours. Together, the machines R & S can finish the job in \(\frac{(36*18)}{(36+18)}= 12 Hours\) In other words, 1 machine of R + 1 machine of S can finish the job together in = 12 Hours

So, to finish the job in 2 Hours, company needs 6 machines of each type - Option C

Re: A company has two types of machines, type R and type S [#permalink]
10 Jan 2014, 09:24

enigma123 wrote:

A company has two types of machines, type R and type S. Operating at a constant rate, a machine of type R does a certain job in 36 hrs and a 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?

Re: A company has two types of machines, type R and type S [#permalink]
25 Nov 2014, 13:51

Could someone please clarify why the answer is not 3 each? I understand how to get to 6 machines and do it quickly but why isn't this 6 machines total since it is a combined rate?

Re: A company has two types of machines, type R and type S [#permalink]
26 Nov 2014, 04:15

1

This post received KUDOS

Expert's post

mns18051985 wrote:

Could someone please clarify why the answer is not 3 each? I understand how to get to 6 machines and do it quickly but why isn't this 6 machines total since it is a combined rate?

x in the solution HERE is the number of type R machines as well as the number of type S machines (we are told that the company used the same number of each type of machine to do the job ). So, when we solve for x, we get what we want. _________________

Re: A company has two types of machines, type R and type S [#permalink]
26 Nov 2014, 05:01

Rate of machine R =1/36 Rate of machine S =1/18

since same no of machines used for R and S to do the same work in 2 hrs So collective rate needed to finish the work in 2 hrs= 1/2 Let the no of machine be x

Re: A company has two types of machines, type R and type S [#permalink]
26 Nov 2014, 20:30

2

This post received KUDOS

R finishes job in 36h and S does the same in 18h. So if both work together, the job will be done in 12h: 1/36 + 1/18 will give you 1/12. Now if one pair of R & S finishes job in 12h, how many such pairs are needed to finish the same job in 2h? 12/2 = 6 pairs of R & S. Hence 6 of R machines are required.

Re: A company has two types of machines, type R and type S [#permalink]
10 Jan 2015, 11:23

Doubt....

1 machine A and 1 machine B together do 1/12 of the job in 1 hour.

We need to do 6/12 of the job in 1 hour... So 6 A machines and 6 B machines will be needed for 6/12 job in 1 hour... and 12 A and B machines will do 12/12 of the job in 2 hours...

Re: A company has two types of machines, type R and type S [#permalink]
11 Jan 2015, 10:47

Expert's post

gmathopeful90 wrote:

Doubt....

1 machine A and 1 machine B together do 1/12 of the job in 1 hour.

We need to do 6/12 of the job in 1 hour... So 6 A machines and 6 B machines will be needed for 6/12 job in 1 hour... and 12 A and B machines will do 12/12 of the job in 2 hours...

Shouldn't the answer be E)12

6 A's and 6 B's do half of the job in 1 hour, so 6 A's and 6 B's will do the whole job in 2 hour and this is what we are asked to find. _________________

Re: A company has two types of machines, type R and type S [#permalink]
11 Jan 2015, 10:58

Bunuel wrote:

gmathopeful90 wrote:

Doubt....

1 machine A and 1 machine B together do 1/12 of the job in 1 hour.

We need to do 6/12 of the job in 1 hour... So 6 A machines and 6 B machines will be needed for 6/12 job in 1 hour... and 12 A and B machines will do 12/12 of the job in 2 hours...

Shouldn't the answer be E)12

6 A's and 6 B's do half of the job in 1 hour, so 6 A's and 6 B's will do the whole job in 2 hour and this is what we are asked to find.

Clear...... simple... thanks a ton.

gmatclubot

Re: A company has two types of machines, type R and type S
[#permalink]
11 Jan 2015, 10:58

This week went in reviewing all the topics that I have covered in my previous study session. I reviewed all the notes that I have made and started reviewing the Quant...

I was checking my phone all day. I wasn’t sure when I would receive the admission decision from Tepper. I received an acceptance from Goizueta in the early morning...

I started running as a cross country team member since highshcool and what’s really awesome about running is that...you never get bored of it! I participated in...