Last visit was: 20 Nov 2025, 08:01 It is currently 20 Nov 2025, 08:01
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 
User avatar
Basshead
User avatar
Joined: 09 Jan 2020
Last visit: 07 Feb 2024
Posts: 925
Own Kudos:
302
 [1]
Given Kudos: 432
Location: United States
Posts: 925
Kudos: 302
 [1]
Machines X and Y work at their respective constant rates. How many mor 09 Dec 2020, 11:39
Kudos
Add Kudos
1
Bookmarks
Bookmark this Post
ravitejapandiri
Machines X and Y work at their respective constant rates. How many more hours does it take machine Y, working alone, to fill a production order of a certain size than it takes machine X, working alone?

(1) Machines X and Y, working together, fill a production order of this size in two-thirds the time that machine X, working alone, does

(2) Machine Y, working alone, fills a production order of this size in twice the time that machine X, working alone, does

Show Spoiler
Can you explain this one Bunuel plz?

At the end,we are having a definite quantity "X"..Right?So I still feel the answer is D.

Because there is no other value/variable affecting the outcome except for the "X".Please clarify if I am going badly wrong somewhere!

Attachment:
DS-3 (1).jpg
Show more

Machine X rate = \(\frac{1}{X}\)
Machine Y rate = \(\frac{1}{Y}\)
Combined rate = \(\frac{X+Y}{XY}\)

Combined time taken = \(\frac{XY }{ X+Y}\)

(1) Tells us that \(\frac{XY }{ X+Y} = \frac{2X}{3}\)

This tells us \(2X = Y\); INSUFFICIENT.

(2) This statement tells us that \(2X = Y\); INSUFFICIENT.

(1&2) Each statement tells us the same information; INSUFFICIENT.

Answer is E.
User avatar
Hoozan
User avatar
Joined: 28 Sep 2018
Last visit: 19 Nov 2025
Posts: 685
Own Kudos:
702
Given Kudos: 248
GMAT 1: 660 Q48 V33 (Online)
GMAT 2: 700 Q49 V37
Products:
My Reviews
GMAT 2: 700 Q49 V37
Posts: 685
Kudos: 702
Machines X and Y work at their respective constant rates. How many mor 09 Feb 2021, 00:48
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Similar Question: https://gmatclub.com/forum/machines-y-a ... 48321.html
avatar
Telo
avatar
Joined: 04 Sep 2020
Last visit: 05 Apr 2021
Posts: 16
Own Kudos:
2
Given Kudos: 140
Posts: 16
Kudos: 2
Machines X and Y work at their respective constant rates. How many mor 11 Feb 2021, 07:13
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Hi Bunuel,
Thank you for the detailed explanation. I got the y=2x for 1) and 2) , so I thought those both are sufficient and chose D(or may be I chose C which is definitely wrong). I should have tried to apply y=2x in xy/(x+y) = x*(2/3), then I would have known it is not sufficient and must have chosen E. But thank you for the explanations, now I know why my answer is wrong and why E is the right answer.
User avatar
avigutman
User avatar
Joined: 17 Jul 2019
Last visit: 30 Sep 2025
Posts: 1,293
Own Kudos:
1,931
Given Kudos: 66
Location: Canada
Schools: NYU Stern (WA)
GMAT 1: 780 Q51 V45
GMAT 2: 780 Q50 V47
GMAT 3: 770 Q50 V45
Expert
Expert reply
Schools: NYU Stern (WA)
GMAT 3: 770 Q50 V45
Posts: 1,293
Kudos: 1,931
Machines X and Y work at their respective constant rates. How many mor 03 Apr 2021, 19:57
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Video solution from Quant Reasoning starts at 23:15
Subscribe for more: https://www.youtube.com/QuantReasoning? ... irmation=1
User avatar
custodio
User avatar
Joined: 25 Jun 2018
Last visit: 03 Feb 2023
Posts: 39
Own Kudos:
10
Given Kudos: 46
Posts: 39
Kudos: 10
Machines X and Y work at their respective constant rates. How many mor 15 Dec 2022, 07:03
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Bunuel

I know this is a silly question but I want to ask:

The general formula is,
\(\frac{1}{x} + \frac{1}{y} = \frac{1}{x+y}\)

where,
machine X takes \(x\) hours -> rate of X = \(\frac{1}{x}\)
machine Y takes \(y\) hours -> rate of Y = \(\frac{1}{y}\)
machine X and Y together take \(x+y\) hours -> rate of X and Y = \(\frac{1}{x+y}\)

(1) says that
\(x+y = \frac{2x}{3} \)

No?
User avatar
Bunuel
User avatar
Math Expert
Joined: 02 Sep 2009
Last visit: 20 Nov 2025
Posts: 105,420
Own Kudos:
778,537
 [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: 105,420
Kudos: 778,537
 [1]
Machines X and Y work at their respective constant rates. How many mor 15 Dec 2022, 07:14
1
Kudos
Add Kudos
Bookmarks
Bookmark this Post
custodio
Bunuel

I know this is a silly question but I want to ask:

The general formula is,
\(\frac{1}{x} + \frac{1}{y} = \frac{1}{x+y}\)

where,
machine X takes \(x\) hours -> rate of X = \(\frac{1}{x}\)
machine Y takes \(y\) hours -> rate of Y = \(\frac{1}{y}\)
machine X and Y together take \(x+y\) hours -> rate of X and Y = \(\frac{1}{x+y}\)

(1) says that
\(x+y = \frac{2x}{3} \)

No?
Show more

No. If machine X takes x hours to do the job, and machine Y takes y hours to do the job, then when working together they should take less time then individually to do the job, no? So, how it can be x + y hours?

The rate of machine X is 1/x and the rate of machine Y is 1/y. The combined rate of the machines is 1/x + 1/y = (x + y)/(xy). Thus, the time they need when working together to do the job is xy/(x + y) (time is the reciprocal of rate).

Hope it's clear.
User avatar
Can,Will
User avatar
Joined: 17 May 2018
Last visit: 05 Apr 2025
Posts: 180
Own Kudos:
39
Given Kudos: 138
Location: India
Schools: IIM
Products:
My Reviews
Schools: IIM
Posts: 180
Kudos: 39
Machines X and Y work at their respective constant rates. How many mor 19 Jan 2023, 00:14
Kudos
Add Kudos
Bookmarks
Bookmark this Post
Dear experts,suggest if following approach is correct or not ?
Attachments

IMG_4983.JPG
IMG_4983.JPG [ 1.85 MiB | Viewed 1155 times ]

User avatar
RastogiSarthak99
User avatar
Joined: 20 Mar 2019
Last visit: 10 Aug 2024
Posts: 141
Own Kudos:
23
Given Kudos: 282
Location: India
Posts: 141
Kudos: 23
Machines X and Y work at their respective constant rates. How many mor 18 Jan 2024, 05:45
Kudos
Add Kudos
Bookmarks
Bookmark this Post
I believe the key here is that the question is referencing HOURS and the options just mention relation to TIME. no units. This time could be seconds, minutes, hours, etc. Without any given values one can't answer number of hours..
User avatar
Suyash1331
User avatar
Joined: 01 Jul 2023
Last visit: 20 Oct 2025
Posts: 118
Own Kudos:
61
Given Kudos: 22
Location: India
Schools: IIMA '26 IIM IIM Calcutta '26 Judge '26 ISB '27 Said '27
GMAT Focus 1: 575 Q65 V70 DI70
GMAT 1: 250 Q20 V34
GPA: 7
Products:
My Reviews
Schools: IIMA '26 IIM IIM Calcutta '26 Judge '26 ISB '27 Said '27
GMAT Focus 1: 575 Q65 V70 DI70
GMAT 1: 250 Q20 V34
Posts: 118
Kudos: 61
Machines X and Y work at their respective constant rates. How many mor 06 Feb 2025, 20:22
Kudos
Add Kudos
Bookmarks
Bookmark this Post
straightaway by looking at statements we can see that both the statements are only giving information regarding x and y in relative terms. there is no new value we can find out. so clearly E is the right answer choice
   1   2 
Moderators:
Bunuel
Math Expert
105420 posts
kingbucky
496 posts