Last visit was: 20 Nov 2025, 04:16 It is currently 20 Nov 2025, 04:16
Home
GMAT
Messages
Tests
Schools
Events
Rewards
Chat
My Profile
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.
Go to My Error Log Learn more
Close
Request Expert Reply
Confirm Cancel
Back to Forum
Create Topic
   1   2 
avatar
diksav
avatar
Current Student
Joined: 13 Sep 2019
Last visit: 17 Apr 2022
Posts: 25
Own Kudos:
4
Given Kudos: 165
Location: India
Schools: McDonough'23 (A) Ross '24 (I) Kellogg '24 (D)
GMAT 1: 720 Q49 V40
GMAT 2: 680 Q48 V34
GRE 1: Q167 V164
GPA: 3.98
Schools: McDonough'23 (A) Ross '24 (I) Kellogg '24 (D)
GMAT 2: 680 Q48 V34
GRE 1: Q167 V164
Posts: 25
Kudos: 4
D01-29 03 Dec 2019, 11:01
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
Rahulbh95
User avatar
Joined: 22 May 2019
Last visit: 06 Apr 2024
Posts: 4
Own Kudos:
7
Given Kudos: 349
Concentration: Technology, Leadership
Schools: INSEAD '26
GMAT 1: 710 Q50 V36 (Online)
WE:Information Technology (Computer Software)
Schools: INSEAD '26
GMAT 1: 710 Q50 V36 (Online)
Posts: 4
Kudos: 7
D01-29 23 Jan 2020, 09:15
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
avatar
rudy15
avatar
Joined: 22 Aug 2020
Last visit: 24 Jun 2024
Posts: 8
Own Kudos:
2
Given Kudos: 9
Location: India
Schools: LSE MFin "22 (S) LBS MFA "22 Imperial MFin "22 Oxford MFE "22 LBS MiM "23
GMAT 1: 710 Q49 V37
GPA: 3.5
Schools: LSE MFin "22 (S) LBS MFA "22 Imperial MFin "22 Oxford MFE "22 LBS MiM "23
GMAT 1: 710 Q49 V37
Posts: 8
Kudos: 2
D01-29 04 Dec 2021, 04:05
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
theGisforGorilla
User avatar
Joined: 02 Feb 2023
Last visit: 28 Apr 2024
Posts: 40
Own Kudos:
23
Given Kudos: 47
GMAT 1: 780 Q49 V49
GMAT 1: 780 Q49 V49
Posts: 40
Kudos: 23
D01-29 04 Mar 2023, 11:33
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 20 Nov 2025
Posts: 105,410
Own Kudos:
778,477
Given Kudos: 99,987
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,410
Kudos: 778,477
D01-29 04 Mar 2023, 12:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I have edited the question and the solution by adding more details to enhance its clarity. I hope it is now easier to understand.
User avatar
Sabi33
User avatar
Joined: 19 May 2023
Last visit: 21 Dec 2023
Posts: 1
Location: Kazakhstan
Schools: Goizueta '27 (S) Jones '27 (S) Kenan-Flagler '27 (S)
Schools: Goizueta '27 (S) Jones '27 (S) Kenan-Flagler '27 (S)
Posts: 1
Kudos: 0
D01-29 19 May 2023, 13:08
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
BottomJee
User avatar
Retired Moderator
Joined: 05 May 2019
Last visit: 09 Jun 2025
Posts: 996
Own Kudos:
1,328
Given Kudos: 1,009
Affiliations: GMAT Club
Location: India
GMAT Focus 1: 645 Q82 V81 DI82
GMAT 1: 430 Q31 V19
GMAT 2: 570 Q44 V25
GMAT 3: 660 Q48 V33
GPA: 3.26
WE:Engineering (Manufacturing)
Products:
My Reviews
GMAT Focus 1: 645 Q82 V81 DI82
GMAT 3: 660 Q48 V33
Posts: 996
Kudos: 1,328
D01-29 12 Aug 2023, 09:37
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
envoyblade
User avatar
Joined: 09 Sep 2024
Last visit: 19 Nov 2025
Posts: 42
Own Kudos:
3
Given Kudos: 3
Location: India
Schools: Darden '26 (I) Tuck '26 (S)
Schools: Darden '26 (I) Tuck '26 (S)
Posts: 42
Kudos: 3
D01-29 08 Oct 2024, 10:12
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
juansecalderon
User avatar
Joined: 15 Sep 2024
Last visit: 25 Feb 2025
Posts: 6
Own Kudos:
2
Given Kudos: 1
Posts: 6
Kudos: 2
D01-29 05 Nov 2024, 18:51
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a high-quality question and I agree with explanation.
User avatar
SergejK
User avatar
Joined: 22 Mar 2024
Last visit: 02 May 2025
Posts: 162
Own Kudos:
781
Given Kudos: 74
Posts: 162
Kudos: 781
D01-29 14 Nov 2024, 06:29
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel: If we know that T/M+T/J + R/J=1 and we also know that both did the same job, can't we equate T/M=T/J + R/J? If yes, couldn't we just solve for R/J=T/M-T/J and then use it in our initial equation providing T/M+T/J + T/M-T/J=1 leading to 2T/M=1 so that either information about T or M would be sufficient to solve for all variables? Then S1 would be sufficient. Where did I go wrong?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 20 Nov 2025
Posts: 105,410
Own Kudos:
778,477
 [1]
Given Kudos: 99,987
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,410
Kudos: 778,477
 [1]
D01-29 14 Nov 2024, 07:34
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
SergejK


Bunuel
Official Solution:


Mac can complete a job in \(M\) days and Jack can complete the same job in \(J\) days. After working together for \(T\) days, Mac left and Jack worked alone to complete the remaining work in \(R\) days. If Mac and Jack completed an equal amount of work, how many days would it take Jack to complete the entire job working alone?

Mac can complete the job in \(M\) days, which means his rate is \(\frac{1}{M}\) job/day.;

Jack can complete the job in \(J\) days, which means his rate is \(\frac{1}{J}\) job/day.

After working together for \(T\) days, Mac left and Jack worked alone to complete the remaining work in \(R\) days. Therefore, Mac worked for \(T\) days only and completed \(\frac{T}{M}\) part of the job, while Jack worked for \(T+R\) days and completed \(\frac{T+R}{J}\) part of the job.

Since Mac and Jack completed an equal amount of work (which means each of them did half of the job), then \(\frac{T}{M}=\frac{1}{2}\) and \(\frac{T+R}{J}=\frac{1}{2}\). Solving for \(T\) gives \(T=\frac{M}{2}\) and \(T=\frac{J}{2}-R\). Therefore, \(\frac{M}{2}=\frac{J}{2}-R\), which simplifies to \(J=M+2R\).

(1) \(M = 20\) days. Not sufficient, we still need the value of \(R\).

(2) \(R = 10\) days. Not sufficient, we still need the value of \(M\).

(1)+(2) Using the equation \(J=M+2R\) and the values \(M=20\) and \(R=10\), we can solve for \(J\) to get \(J=40\). Therefore, Jack would need \(J=40\) days to complete the entire job working alone. Sufficient.


Answer: C
Bunuel: If we know that T/M+T/J + R/J=1 and we also know that both did the same job, can't we equate T/M=T/J + R/J? If yes, couldn't we just solve for R/J=T/M-T/J and then use it in our initial equation providing T/M+T/J + T/M-T/J=1 leading to 2T/M=1 so that either information about T or M would be sufficient to solve for all variables? Then S1 would be sufficient. Where did I go wrong?
Show more

Yes, as shown in the solution, we can get \(T = \frac{M}{2}\) (and \(T = \frac{J}{2} - R\)) from the stem. However, from (1), we would still only know M and T, while J and R would remain unknown. Notice that 10/20 + 10/J + R/J = 1 and 10 = J/2 - R are essentially the same equations (simplifying 10/20 + 10/J + R/J = 1 gives 10 = J/2 - R), so you cannot solve for J and R.

Hope it's clear.
User avatar
chandan_13
User avatar
Joined: 30 Sep 2016
Last visit: 28 Aug 2025
Posts: 9
Own Kudos:
8
Given Kudos: 13
Posts: 9
Kudos: 8
D01-29 16 Jan 2025, 14:27
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I like the solution - it’s helpful.
User avatar
cromander
User avatar
Joined: 24 May 2025
Last visit: 04 Jun 2025
Posts: 1
Given Kudos: 8
Posts: 1
Kudos: 0
D01-29 02 Jun 2025, 05:35
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I like the solution - it’s helpful.
User avatar
PrateekSood
User avatar
Joined: 24 Mar 2025
Last visit: 09 Nov 2025
Posts: 6
Own Kudos:
3
Given Kudos: 6
Location: India
Schools: ISB '26 HEC Sept '26
GMAT Focus 1: 645 Q85 V81 DI80
GPA: 8.9
Schools: ISB '26 HEC Sept '26
GMAT Focus 1: 645 Q85 V81 DI80
Posts: 6
Kudos: 3
D01-29 04 Jul 2025, 22:58
Kudos
Add Kudos
Bookmarks
Bookmark this Post
This is a great question that’s helpful for learning.
User avatar
Chakrawarty
User avatar
Joined: 17 Feb 2025
Last visit: 25 Aug 2025
Posts: 19
Own Kudos:
1
Given Kudos: 41
Location: India
Schools: INSEAD Jan '27 Booth '27 HEC Sept '27
GPA: 9.35
Schools: INSEAD Jan '27 Booth '27 HEC Sept '27
Posts: 19
Kudos: 1
D01-29 05 Jul 2025, 07:48
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Thanks, this explanation really helped. I was stuck with an extra variable while solving this.
Bunuel
Official Solution:


Mac can complete a job in \(M\) days and Jack can complete the same job in \(J\) days. After working together for \(T\) days, Mac left and Jack worked alone to complete the remaining work in \(R\) days. If Mac and Jack completed an equal amount of work, how many days would it take Jack to complete the entire job working alone?

Mac can complete the job in \(M\) days, which means his rate is \(\frac{1}{M}\) job/day.;

Jack can complete the job in \(J\) days, which means his rate is \(\frac{1}{J}\) job/day.

After working together for \(T\) days, Mac left and Jack worked alone to complete the remaining work in \(R\) days. Therefore, Mac worked for \(T\) days only and completed \(\frac{T}{M}\) part of the job, while Jack worked for \(T+R\) days and completed \(\frac{T+R}{J}\) part of the job.

Since Mac and Jack completed an equal amount of work (which means each of them did half of the job), then \(\frac{T}{M}=\frac{1}{2}\) and \(\frac{T+R}{J}=\frac{1}{2}\). Solving for \(T\) gives \(T=\frac{M}{2}\) and \(T=\frac{J}{2}-R\). Therefore, \(\frac{M}{2}=\frac{J}{2}-R\), which simplifies to \(J=M+2R\).

(1) \(M = 20\) days. Not sufficient, we still need the value of \(R\).

(2) \(R = 10\) days. Not sufficient, we still need the value of \(M\).

(1)+(2) Using the equation \(J=M+2R\) and the values \(M=20\) and \(R=10\), we can solve for \(J\) to get \(J=40\). Therefore, Jack would need \(J=40\) days to complete the entire job working alone. Sufficient.


Answer: C
Show more
User avatar
Alasoy
User avatar
Joined: 02 Jan 2025
Last visit: 17 Nov 2025
Posts: 17
Own Kudos:
2
Given Kudos: 18
Location: Indonesia
GPA: 3.15
WE:Business Development (Retail: E-commerce)
Posts: 17
Kudos: 2
D01-29 02 Sep 2025, 08:19
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I think this is a very high quality questions and needs to read every single details in order to follow the logic (e.g. Mac and Jack used to work together, they work on a same proportion)

after you translate every single variable into algebra the question become easier to solve
User avatar
MegB07
User avatar
Joined: 15 Sep 2022
Last visit: 19 Nov 2025
Posts: 55
Own Kudos:
2
Given Kudos: 43
Location: India
Products:
GMAT Club Tests
Posts: 55
Kudos: 2
D01-29 27 Sep 2025, 23:27
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I did not quite understand the solution. When both are working together, then shouldnt it be (1/M + 1/J)T = 1/2 and when mac lefts Jack completes remaining half of the work in 1/J*R = 1/2 so R is sufficient to answer.

Please tell where am i going wrong
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 20 Nov 2025
Posts: 105,410
Own Kudos:
778,477
 [1]
Given Kudos: 99,987
Products:
GMAT Club Tests Forum Quiz
Expert
Expert reply
Active GMAT Club Expert! Tag them with @ followed by their username for a faster response.
Posts: 105,410
Kudos: 778,477
 [1]
D01-29 27 Sep 2025, 23:48
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
MegB07
I did not quite understand the solution. When both are working together, then shouldnt it be (1/M + 1/J)T = 1/2 and when mac lefts Jack completes remaining half of the work in 1/J*R = 1/2 so R is sufficient to answer.

Please tell where am i going wrong
Show more
The mistake is thinking that (1/M + 1/J)T = 1/2. That would mean their combined work in T days is half the job. But the problem states each of them did exactly half on his own.

That is why the official solution sets T/M = 1/2 for Mac and (T + R)/J = 1/2 for Jack. Those conditions guarantee both completed equal shares.
   1   2 
Moderators:
Bunuel
Math Expert
105410 posts
bb
Founder
42395 posts