Find all School-related info fast with the new School-Specific MBA Forum

It is currently 12 Jul 2014, 08:04

Close

GMAT Club Daily Prep

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.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

Combining work rates (other ways to solve these problems?)

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
Intern
Intern
avatar
Joined: 22 Jan 2005
Posts: 15
Followers: 0

Kudos [?]: 0 [0], given: 0

Combining work rates (other ways to solve these problems?) [#permalink] New post 22 Jan 2005, 10:08
How do you solve the fractional expression in the first problem?
What other ways are there to solve this type of problem?

Q: If Tom can do a job in 10 hours and Tom and Mary can do the job in 6 hours working at their respective rates, how long will it take Mary to do the job by herself.

I know of two possible ways to solve this.

(1) Using the (X*Y)/(X+Y) formula I came up with:

(10*M)/(10+M) = 6

Where T=X=10 and Y=M. And because my math skills are rusty I don't know where to go from here. Am I cross multiplying the fractional expression?

(2) Using the Princeton method of pie charts:

Tom = w=120
r=12/hr | t=10hrs


Tom and Mary = w=120
r=10 + M? | t=6hrs


Mary = w=120
r= 10/hr | t= 12hrs

I got the question right after plugging in any Work value that is a multiple of 6 and 10; 60, 120, etc.
Director
Director
avatar
Joined: 19 Nov 2004
Posts: 565
Location: SF Bay Area, USA
Followers: 3

Kudos [?]: 25 [0], given: 0

GMAT Tests User
 [#permalink] New post 22 Jan 2005, 12:39
Rate problems can be tackled easily, if you follow a method.
A simple way to do Rate problems is to use the following formula:

X1/T1 + X2/T2 = J

X1= Time spent together by A
X2 = Time spent together by B
T1 = Time spent alone by A
T2 = Time spent alond by B
J= Fraction of job

Here, X1 =6, X2= 6, T1=10, T2 = unknown, J= 1 (full job)
=> T2 = 15
(This problem could be solved in about 30 second with this method).
This formula can be used for almost all rate problems, including the one that involves many people once you think through the problem and obtain the correct parameters to plug it into the above equation. In GMAT this will help in terms of time!

See another rate problem that is solved easily using this formula at http://www.gmatclub.com/phpbb/viewtopic.php?t=13304
Director
Director
User avatar
Joined: 07 Jun 2004
Posts: 620
Location: PA
Followers: 2

Kudos [?]: 127 [0], given: 22

GMAT Tests User
 [#permalink] New post 22 Jan 2005, 12:46
my advice to u is work leess on the formula undrstand the concept of rate and work that will help u and tackle complicated problmes . cuz GMAT Will not give u straight forward problomes where u can plug numbers in a formula

work on fundamentals it may take time but it will stick in your brain!!

thts my opinion
SVP
SVP
User avatar
Joined: 03 Jan 2005
Posts: 2255
Followers: 12

Kudos [?]: 186 [0], given: 0

GMAT Tests User
 [#permalink] New post 22 Jan 2005, 21:30
Let say Tom's working rate is t and Mary's working rate is m.

10t=6(t+m)
4t=6m
=>10t=15m

In other words, the work that Tom can finish in 10 hours, Mary will need 15 hours to finish it.

It's quite similar to distance problem, actually.
Director
Director
avatar
Joined: 27 Dec 2004
Posts: 910
Followers: 1

Kudos [?]: 10 [0], given: 0

GMAT Tests User
 [#permalink] New post 07 Feb 2005, 09:09
HongHu wrote:
Let say Tom's working rate is t and Mary's working rate is m.

10t=6(t+m)
4t=6m
=>10t=15m

In other words, the work that Tom can finish in 10 hours, Mary will need 15 hours to finish it.

It's quite similar to distance problem, actually.


Here is another approach:

Tom can do a job in 10 hours means he doesn 1/10 of the job in an hour

Tom and Mary can do the same job in 6 hours means they both can get 1/6 of the job done in an hour.

To find Mary’s rate (M), then the sum of their rate per hour = their rate combined per hour.

1/10 + 1/M = 1/6.
1/M = 4/60 (note that this is the time it takes marry per hour)
Take the reciprocal of this fraction and you will get the time it takes marry to complete the same job alone = 60 / 4 = 15 hours.

I hope that helps.
Intern
Intern
avatar
Joined: 19 Dec 2004
Posts: 14
Followers: 0

Kudos [?]: 0 [0], given: 0

GMAT Tests User
 [#permalink] New post 25 Mar 2005, 21:09
Nocilis, could you give an example using your method of solving?
Intern
Intern
avatar
Joined: 25 Feb 2005
Posts: 42
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 25 Mar 2005, 23:32
1/T + 1/M = 1/6

1/10 + 1/M = 1/6

1/M = 1/6-1/10
1/M = 4/60 = 1/12

M = 12 hr
Intern
Intern
avatar
Joined: 25 Feb 2005
Posts: 42
Followers: 1

Kudos [?]: 1 [0], given: 0

 [#permalink] New post 25 Mar 2005, 23:35
scorer wrote:
1/T + 1/M = 1/6

1/10 + 1/M = 1/6

1/M = 1/6-1/10
1/M = 4/60 = 1/12

M = 12 hr


oops! i mean M=15 hr.
Intern
Intern
avatar
Joined: 14 Aug 2003
Posts: 7
Location: Texas
Followers: 0

Kudos [?]: 0 [0], given: 0

TO HongHu [#permalink] New post 26 Mar 2005, 07:39
HEllo HH, I am trying to learn all the different methods to solve this, but I missed a step in your solution.

How did you go from: 4t=6m to 10t=15m
ThanksTP
Manager
Manager
avatar
Joined: 17 Dec 2004
Posts: 74
Followers: 2

Kudos [?]: 3 [0], given: 0

Re: TO HongHu [#permalink] New post 27 Mar 2005, 21:51
texaspunk wrote:
HEllo HH, I am trying to learn all the different methods to solve this, but I missed a step in your solution.

How did you go from: 4t=6m to 10t=15m
ThanksTP


10t=6(t+m)
4t=6m
t=1.5m

Here, you get the ratio of Tom's work to Mary's work. Knowing that Tom takes 10 hours, you plug that in to the ratio and get 15 for Mary.

I would probably go about it like Folaa3 does... I usually figure out how much of a job each can do in an hour...
SVP
SVP
User avatar
Joined: 03 Jan 2005
Posts: 2255
Followers: 12

Kudos [?]: 186 [0], given: 0

GMAT Tests User
 [#permalink] New post 28 Mar 2005, 08:39
halahpeno is right. Though I would try to avoid fractions and/or decimals in the test to save time. So what I'd do is this:

4t=6m
2t=3m (divided both sides by 2)
10t=15m (multiply both sides by 5)

:)
  [#permalink] 28 Mar 2005, 08:39
    Similar topics Author Replies Last post
Similar
Topics:
Faster way to solve this rates problem? Liquidus 1 24 Aug 2011, 21:00
Problem solving work problem rite2deepti 2 30 Nov 2010, 06:03
2 Experts publish their posts in the topic Combined Work/Rates Problems Strategy? Superprime 4 09 Oct 2009, 07:33
Problem Solving: Combinations vsaxena 6 07 Jul 2007, 09:44
Combination Problem Solving stretchad 2 12 Dec 2005, 07:34
Display posts from previous: Sort by

Combining work rates (other ways to solve these problems?)

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

Powered by phpBB © phpBB Group and phpBB SEO

Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.