GMAT Question of the Day - Daily to your Mailbox; hard ones only

It is currently 22 Sep 2018, 11:56

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.

Close

Request Expert Reply

Confirm Cancel

A and B together can do a peace of work in 12 days,which B

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Intern
Intern
User avatar
Joined: 03 Jan 2006
Posts: 28
A and B together can do a peace of work in 12 days,which B  [#permalink]

Show Tags

New post 05 Feb 2007, 11:30
A and B together can do a peace of work in 12 days,which B and C together can do in 16 days.After A has been working at it for 5 Days and B for 7 Days,C finishes in 13 days.In how many days C alone will do the work?

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.


If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.
VP
VP
User avatar
Joined: 09 Jan 2007
Posts: 1044
Location: New York, NY
Schools: Chicago Booth Class of 2010
  [#permalink]

Show Tags

New post 05 Feb 2007, 12:18
I Think this PS would be easily solved by changing the answers in the equations. Don't you have them?
Senior Manager
Senior Manager
User avatar
Joined: 04 Jan 2006
Posts: 275
Re: A and B and C  [#permalink]

Show Tags

New post 05 Feb 2007, 12:48
1
sravan_m444 wrote:
A and B together can do a peace of work in 12 days,which B and C together can do in 16 days.After A has been working at it for 5 Days and B for 7 Days,C finishes in 13 days.In how many days C alone will do the work?


Assuming everybody works at constant rate and independent from each other.

When A works for 5 days and B works for 7 days, we can conclude that A and B work together for 5 days and B works alone for 2 days. And

Work Rate(A+B) = 1/12 (work/day)

Thus, Work is done by A and B for 5 days together = 5 days x 1/12 (work/day) = 5/12 work

When B works for 7-5 = 2 days and C works for 13 day, we can conclude that B and C work together for 2 days and C work alone for 13 - 2 = 11 days.

Work Rate(B+C) = 1/16 (work/day)

Thus, Work is done by B and C for 2 days = 2 days x 1/16 (work/day) = 1/8 work

The remaining job = 1 - 5/12 - 1/8 = (24 - 10 - 3)/24 = 11/24 work

C can finish this part of work within 11 days. Therefore, the work rate for C = 11/24 (work) x 1/11(1/day) = 1/24 (work/day)

Or C can finish one work in = 24 days

Hope this is right. :P
Intern
Intern
avatar
Joined: 20 Jan 2007
Posts: 17
  [#permalink]

Show Tags

New post 05 Feb 2007, 14:59
nice answer devilmirror, but i'm not sure if it accurately represents the stem:

"After A has been working at it for 5 Days and B for 7 Days", then C has 13 days left...

It seems to me that A,B and C work as in a sequence: first A, second B and then C.

ARe you sure that A and B can work together?
Manager
Manager
avatar
Joined: 10 Dec 2005
Posts: 111
  [#permalink]

Show Tags

New post 05 Feb 2007, 15:16
I solved it like this

Let's say rate of A is R1 work/day,
rate of B is R2 work/day, and
rate of C is R3 work/day

Based on the information we have we know that

R1 + R2 = 1/12 ---------------------- 1
R2 + R3 = 1/16----------------------- 2
5R1 + 7R2 + 13R3 = 1 -------------- 3

Let's solve equation 3 for R2

5(1/12 - R2) + 7R2 + 13(1/16 - R2) = 1

5/12 - 5R2 + 7R2 + 13/16 - 13R2 = 1

5/12 + 13/16 -11R2 = 1

Therefore, 11R2 = 5/12 + 13/16
R2 = 1/11(5/12 + 13/16)
R2 = 0.11

We need to find R3 though, we know from 2 that
R3 = 1/16 - R2
R3 = 1/16 - 0.11
R3 = -0.0475

But rate cannot be negative hence
R3 = 0.0475 w/day
Hence in order to finish 1 work R3 will take 1/0.0475 = 21 days
_________________

"Live as if you were to die tomorrow. Learn as if you were to live forever." - Mahatma Gandhi

Manager
Manager
avatar
Joined: 10 Dec 2005
Posts: 111
  [#permalink]

Show Tags

New post 05 Feb 2007, 15:20
sravan_m444, can you validate the answer please
_________________

"Live as if you were to die tomorrow. Learn as if you were to live forever." - Mahatma Gandhi

Director
Director
avatar
Joined: 12 Jun 2006
Posts: 522
  [#permalink]

Show Tags

New post 05 Feb 2007, 15:30
This is kind of vague (at least for me). Are A,B and C working in succession or in unison?
Manager
Manager
avatar
Joined: 10 Dec 2005
Posts: 111
  [#permalink]

Show Tags

New post 05 Feb 2007, 15:31
I solved it considering succession
_________________

"Live as if you were to die tomorrow. Learn as if you were to live forever." - Mahatma Gandhi

Senior Manager
Senior Manager
User avatar
Joined: 04 Jan 2006
Posts: 275
  [#permalink]

Show Tags

New post 05 Feb 2007, 18:09
pau.sabria wrote:
nice answer devilmirror, but i'm not sure if it accurately represents the stem:

"After A has been working at it for 5 Days and B for 7 Days", then C has 13 days left...

It seems to me that A,B and C work as in a sequence: first A, second B and then C.

ARe you sure that A and B can work together?


Hi pau.sabria,

Altough, A, B, and C work as sequence but you can consider them working to gether on the same days and use the rate provide from the question. Just keep in mind that the time that they work will be 2 time faster.

Here the prove.

Assuming A's work rate = 1/a (work/day)
Assuming B's work rate = 1/b (work/day)


If A works for T day the work that A does = T/a work
If B also works for T day the work that B does = T/b work
Total work done = T/a + T/b


However, if A and B working together they will use T day to finish this job.
Work rate = (T/a + T/b)/T = (1/a + 1/b)
The equation above is the work rate of A + B combined!


Therefore, we can safely conclude that.

If A work on T day and B work on T day seperately, this will equal to A and B working together for T day.

Using the prove above to solve that question and the answer is 24.

:wink:
Manager
Manager
avatar
Joined: 10 Dec 2005
Posts: 111
  [#permalink]

Show Tags

New post 05 Feb 2007, 18:28
devilmirror, Can you look at my solution? I think the answer is 21
_________________

"Live as if you were to die tomorrow. Learn as if you were to live forever." - Mahatma Gandhi

Senior Manager
Senior Manager
User avatar
Joined: 04 Jan 2006
Posts: 275
  [#permalink]

Show Tags

New post Updated on: 05 Feb 2007, 18:36
amorpheus wrote:
I solved it like this

Let's say rate of A is R1 work/day,
rate of B is R2 work/day, and
rate of C is R3 work/day

Based on the information we have we know that

R1 + R2 = 1/12 ---------------------- 1
R2 + R3 = 1/16----------------------- 2
5R1 + 7R2 + 13R3 = 1 -------------- 3

Let's solve equation 3 for R2

5(1/12 - R2) + 7R2 + 13(1/16 - R2) = 1

5/12 - 5R2 + 7R2 + 13/16 - 13R2 = 1

5/12 + 13/16 -11R2 = 1

Therefore, 11R2 = 5/12 + 13/16
R2 = 1/11(5/12 + 13/16)
R2 = 0.11

We need to find R3 though, we know from 2 that
R3 = 1/16 - R2
R3 = 1/16 - 0.11
R3 = -0.0475

But rate cannot be negative hence
R3 = 0.0475 w/day
Hence in order to finish 1 work R3 will take 1/0.0475 = 21 days


Amorpheus, you set the equation correctly but you solved it wrong.

R1 + R2 = 1/12 ---------------------- 1
R2 + R3 = 1/16----------------------- 2
5R1 + 7R2 + 13R3 = 1 -------------- 3

5(1/12 - R2) + 7R2 + 13(1/16 - R2) = 1

5/12 - 5R2 + 7R2 + 13/16 - 13R2 = 1

5/12 + 13/16 -11R2 = 1

Therefore, 11R2 = 5/12 + 13/16 - 1 {you missed -1 this line}
11R2 = (20 + 39 - 48)/48 = 11/48
R2 = 1/48
Therefore R3 = C's work rate = 1/16 - 1/48 = (3-1)/48 = 2/48 = 1/24 (work/day)

C will use 24 days to finish this job.

Same as my answer.

:P

I believe some people may like this method better than mine.

Originally posted by devilmirror on 05 Feb 2007, 18:33.
Last edited by devilmirror on 05 Feb 2007, 18:36, edited 1 time in total.
Manager
Manager
avatar
Joined: 10 Dec 2005
Posts: 111
  [#permalink]

Show Tags

New post 05 Feb 2007, 18:35
oh bummer haste creates waste I always do that... I see it now... yeah I think my method is easy to understand and probably quicker also.

Thanks for pointing that out.
_________________

"Live as if you were to die tomorrow. Learn as if you were to live forever." - Mahatma Gandhi

Senior Manager
Senior Manager
User avatar
Joined: 04 Jan 2006
Posts: 275
  [#permalink]

Show Tags

New post 05 Feb 2007, 18:40
amorpheus wrote:
oh bummer haste creates waste I always do that... I see it now... yeah I think my method is easy to understand and probably quicker also.

Thanks for pointing that out.


:lol: Nah-ah!

I think both methods can solve the question beautifully.
Intern
Intern
User avatar
Joined: 03 Jan 2006
Posts: 28
  [#permalink]

Show Tags

New post 05 Feb 2007, 19:16
Guys answer is 24.I liked both the ways
Non-Human User
User avatar
Joined: 09 Sep 2013
Posts: 8154
Premium Member
Re: A and B together can do a peace of work in 12 days,which B  [#permalink]

Show Tags

New post 13 Jan 2018, 23:06
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.

--== Message from the GMAT Club Team ==--

THERE IS LIKELY A BETTER DISCUSSION OF THIS EXACT QUESTION.
This discussion does not meet community quality standards. It has been retired.


If you would like to discuss this question please re-post it in the respective forum. Thank you!

To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative | Verbal Please note - we may remove posts that do not follow our posting guidelines. Thank you.

_________________

GMAT Books | GMAT Club Tests | Best Prices on GMAT Courses | GMAT Mobile App | Math Resources | Verbal Resources

GMAT Club Bot
Re: A and B together can do a peace of work in 12 days,which B &nbs [#permalink] 13 Jan 2018, 23:06
Display posts from previous: Sort by

A and B together can do a peace of work in 12 days,which B

  post reply Question banks Downloads My Bookmarks Reviews Important topics  

Moderator: chetan2u

Events & Promotions

PREV
NEXT


Copyright

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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.