Machine M, working alone at its constant rate, produces x wi : GMAT Data Sufficiency (DS)
Check GMAT Club Decision Tracker for the Latest School Decision Releases http://gmatclub.com/AppTrack

 It is currently 17 Jan 2017, 05:50

### 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

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

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Machine M, working alone at its constant rate, produces x wi

Author Message
TAGS:

### Hide Tags

Intern
Joined: 24 Jan 2012
Posts: 10
Followers: 0

Kudos [?]: 130 [3] , given: 3

Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

24 Sep 2013, 07:29
3
KUDOS
18
This post was
BOOKMARKED
00:00

Difficulty:

65% (hard)

Question Stats:

58% (02:26) correct 42% (01:28) wrong based on 743 sessions

### HideShow timer Statistics

Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

1) x > 0.8y
2) y = x + 1

My question :

1st statement tells that x/y < 4/5 => this means x's rate is more than y hence its sufficient to answer that machine M produce more widgets than machine N in that time

2nd statement says that y = x + 1
so if x = 2 widgets
then y = 3 widgets
this means that in 20 minutes x will produce 10 widgets and in same time y will produce 12 widgets so we get a definite answer hence its sufficient

Thats why I chose D but the OA is A

[Reveal] Spoiler: OA
Intern
Joined: 07 Aug 2013
Posts: 30
Followers: 0

Kudos [?]: 5 [1] , given: 1

Re: Machine M and Machine N [#permalink]

### Show Tags

24 Sep 2013, 07:46
1
KUDOS
The easiest way to look at the question (imo) is to say that;

Total produced= 20*(X/4)+20*(X/5) => T=5X+4Y

1) If x>0.8y

then T=5*(4y/5)+4Y => T=4y+4y since x is bigger then 0.8y T=(a number higher then 4)y +4y

Sufficient

2) y= x+1

then T=5X+4X+4 => Total M=5X Total N= 4x+4, if x=1 then no if x=1000 then yes

Insufficient
Math Expert
Joined: 02 Sep 2009
Posts: 36531
Followers: 7071

Kudos [?]: 92970 [30] , given: 10541

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

25 Sep 2013, 01:40
30
KUDOS
Expert's post
11
This post was
BOOKMARKED
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.
_________________
Manager
Joined: 14 Jan 2013
Posts: 154
Concentration: Strategy, Technology
GMAT Date: 08-01-2013
GPA: 3.7
WE: Consulting (Consulting)
Followers: 3

Kudos [?]: 247 [0], given: 30

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

03 Mar 2014, 00:40
Bunuel wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.

Bunuel,

I am not able to understand statement B. Can you please elaborate...
_________________

"Where are my Kudos" ............ Good Question = kudos

"Start enjoying all phases" & all Sections

__________________________________________________________________
http://gmatclub.com/forum/collection-of-articles-on-critical-reasoning-159959.html

http://gmatclub.com/forum/percentages-700-800-level-questions-130588.html

http://gmatclub.com/forum/700-to-800-level-quant-question-with-detail-soluition-143321.html

Math Expert
Joined: 02 Sep 2009
Posts: 36531
Followers: 7071

Kudos [?]: 92970 [1] , given: 10541

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

03 Mar 2014, 00:43
1
KUDOS
Expert's post
1
This post was
BOOKMARKED
Mountain14 wrote:
Bunuel wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.

Bunuel,

I am not able to understand statement B. Can you please elaborate...

The question asks: is x/4 > y/5 ?

(2) says: y = x + 1. Substitute y = x + 1 into the question: is x/4 > (x+1)/5? --> is x > 4? Since we cannot answer this question, then this statement is not sufficient.

Hope it's clear.
_________________
Moderator
Joined: 20 Dec 2013
Posts: 189
Location: United States (NY)
GMAT 1: 640 Q44 V34
GMAT 2: 710 Q48 V40
GMAT 3: 720 Q49 V40
GPA: 3.16
WE: Consulting (Venture Capital)
Followers: 7

Kudos [?]: 66 [1] , given: 71

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

03 Mar 2014, 20:26
1
KUDOS
M = x/4
N = y/5

5x/20>4y/20 -->
5x>4y?

I.
x>.8y
x>4y/5
5x>4y
Suff

II.
y=x+1
5x>4x+4 ?

x=1/20
1/4 > 1/5 + 4 --> no
x=5
25>24 --> yes

Insuff

A
_________________
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13423
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

28 Mar 2015, 11:17
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.
_________________
EMPOWERgmat Instructor
Status: GMAT Assassin/Co-Founder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 8269
Location: United States (CA)
GMAT 1: 800 Q51 V49
GRE 1: 340 Q170 V170
Followers: 379

Kudos [?]: 2455 [1] , given: 163

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

29 Mar 2015, 17:50
1
KUDOS
Expert's post
2
This post was
BOOKMARKED
Hi All,

The way that you choose to organize your notes can often impact how much work you have to do to answer a given GMAT question (as well as the difficulty of the work). As such, part of your practice should really involve proper note-taking and working on the most 'efficient' ways for you to take notes, 'set up' your work, etc.

Here, we're told about the rates of 2 machines:
Machine M can produce X widgets in 4 minutes
Machine N can produce Y widgets in 5 minutes

We're then told that each machine works for 20 minutes. We're asked if Machine M produces more widgets than Machine N during that time.

During those 20 minutes, Machine M will produce 5X widgets and Machine N will produce 4Y widgets. In real simple terms, the question asks "is 5X > 4Y?" This is a YES/NO question. A mix of TESTing VALUES and Algebra will help to answer this question.

Fact 1: X > 0.8Y

We can multiply both sides of this inequality by 10....

10X > 8Y

Then divide both sides by 2...

5X > 4Y

Notice how the question asked "is 5X > 4Y?".... Fact 1 tells us that 5X IS greater than 4Y.
Fact 1 is SUFFICIENT

Fact 2: Y = X + 1

IF....
X = 1
Y = 2
5(1) is NOT > 4(2) and the answer to the question is NO.

IF...
X = 10
Y = 11
5(10) IS > 4(11) and the answer to the question is YES.
Fact 2 is INSUFFICIENT

[Reveal] Spoiler:
A

GMAT assassins aren't born, they're made,
Rich
_________________

# Rich Cohen

Co-Founder & GMAT Assassin

# Special Offer: Save $75 + GMAT Club Tests 60-point improvement guarantee www.empowergmat.com/ ***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!*********************** Manager Joined: 08 Oct 2013 Posts: 52 Followers: 1 Kudos [?]: 14 [1] , given: 16 Re: Machine M, working alone at its constant rate, produces x wi [#permalink] ### Show Tags 05 May 2015, 09:39 1 This post received KUDOS IMHO, this is a fairly easy question but the language will deceive you and you will mark the wrong answer unless you muscle the algebra. I solved by intuition and got it wrong. So basically the question is, "Is the work done by Machine M is greater than the work done by N" (in 20 min) Machine M: T= 4 min, W=x hence rate = x/4 Machine N: T= 5 min, W=y hence Rate = y/5 M will do more work if its rate is more than N so is x/4 > y/5? x > 4/5(y) or is x > 0.8(y) ? - this is the Question Statement 1 is a direct answer Statement 2 becomes: x/4 > y/5? x/4 > (x+1)/5? x/4 > (x+1)/4+1? - this is a general property of ratios. the inequality is true if x<4. Since we don't know the value of x, state2 is insufficient. Answer A EMPOWERgmat Instructor Status: GMAT Assassin/Co-Founder Affiliations: EMPOWERgmat Joined: 19 Dec 2014 Posts: 8269 Location: United States (CA) GMAT 1: 800 Q51 V49 GRE 1: 340 Q170 V170 Followers: 379 Kudos [?]: 2455 [1] , given: 163 Re: Machine M, working alone at its constant rate, produces x wi [#permalink] ### Show Tags 06 May 2015, 10:31 1 This post received KUDOS Expert's post Hi AjChakravarthy, You bring up a number of important points in your post that are worth emphasizing: 1) Many DS questions ARE actually pretty easy, so you shouldn't take any chances when it comes to solving them - do the necessary work and get those points! 2) A Test Taker's "instinct" when dealing with DS question can often be incorrect, so you have to do enough work to PROVE that your instinct is correct. 3) Taking the time to "rewrite" the question can often lead to shortcuts later on in the work. GMAT assassins aren't born, they're made, Rich _________________ # Rich Cohen Co-Founder & GMAT Assassin # Special Offer: Save$75 + GMAT Club Tests

60-point improvement guarantee
www.empowergmat.com/

***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************

Manager
Joined: 08 Oct 2013
Posts: 52
Followers: 1

Kudos [?]: 14 [0], given: 16

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

06 May 2015, 11:08
EMPOWERgmatRichC wrote:
Hi AjChakravarthy,

You bring up a number of important points in your post that are worth emphasizing:

1) Many DS questions ARE actually pretty easy, so you shouldn't take any chances when it comes to solving them - do the necessary work and get those points!

2) A Test Taker's "instinct" when dealing with DS question can often be incorrect, so you have to do enough work to PROVE that your instinct is correct.

3) Taking the time to "rewrite" the question can often lead to shortcuts later on in the work.

GMAT assassins aren't born, they're made,
Rich

GMAT assassins aren't born, they're made, - very powerful.

Training to be one
Veritas Prep GMAT Instructor
Joined: 16 Oct 2010
Posts: 7119
Location: Pune, India
Followers: 2130

Kudos [?]: 13629 [0], given: 222

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

06 May 2015, 19:45
violetsplash wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

1) x > 0.8y
2) y = x + 1

My question :

1st statement tells that x/y < 4/5 => this means x's rate is more than y hence its sufficient to answer that machine M produce more widgets than machine N in that time

2nd statement says that y = x + 1
so if x = 2 widgets
then y = 3 widgets
this means that in 20 minutes x will produce 10 widgets and in same time y will produce 12 widgets so we get a definite answer hence its sufficient

Thats why I chose D but the OA is A

Instead of picking numbers on this question, one might try to sit back and work out the logic of statement 2. It is quite simple once you get down to it.

You want to know whether x/4 > y/5. (x and y are good positive integers so no complications.)
So if x is greater than y, certainly x/4 will be greater than y/5 because x is divided by a smaller number.
If x is smaller than y, then it depends on how much smaller. If x is only slightly smaller than y, then it is possible that x/4 > y/5.

2nd statement says that y = x + 1
So x is 1 smaller than y. Now the problem is that you don't know the values of x and y so you don't know whether this 1 is huge in comparison to x and y or little. Therefore, you cannot say whether x/4 will be smaller or y/5.
_________________

Karishma
Veritas Prep | GMAT Instructor
My Blog

Get started with Veritas Prep GMAT On Demand for \$199

Veritas Prep Reviews

Intern
Joined: 18 May 2014
Posts: 5
Followers: 0

Kudos [?]: 0 [0], given: 2

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

16 Aug 2015, 21:03
Bunuel wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.

Hi Banuel: Is the following reasoning correct/possible to identify statement (2) as sufficient? Reasoning as follows:

Because we know x > 4, it must be at least 5 assuming you can't have a fraction of a widget (i.e. you can't produce 4.5 widgets every 4 minutes). Given that y = x + 1 which yields 6 in this case, then 5/4 > 6/5 is in fact true. Furthermore, this inequality stays true as the value of x increases. Thus, the statement could be sufficient?
Math Expert
Joined: 02 Sep 2009
Posts: 36531
Followers: 7071

Kudos [?]: 92970 [0], given: 10541

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

17 Aug 2015, 00:46
tigrr49 wrote:
Bunuel wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.

Hi Banuel: Is the following reasoning correct/possible to identify statement (2) as sufficient? Reasoning as follows:

Because we know x > 4, it must be at least 5 assuming you can't have a fraction of a widget (i.e. you can't produce 4.5 widgets every 4 minutes). Given that y = x + 1 which yields 6 in this case, then 5/4 > 6/5 is in fact true. Furthermore, this inequality stays true as the value of x increases. Thus, the statement could be sufficient?

No, that's not correct. We can say, for example, that machine M produces 0.5 widgets every 4 minutes, this would mean that to produce 1 widget it needs 8 minutes.
_________________
Senior Manager
Joined: 15 Sep 2011
Posts: 365
Location: United States
WE: Corporate Finance (Manufacturing)
Followers: 6

Kudos [?]: 299 [0], given: 45

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

19 Sep 2015, 11:44
tigrr49 wrote:
Bunuel wrote:
Machine M, working alone at its constant rate, produces x widgets every 4 minutes. Machine N, working alone at its constant rate, produces y widgets every 5 minutes. If machines M and N working simultaneously at their respective constant rates for 20 minutes, does machine M produce more widgets than machine N in that time ?

The rate of M = x/4 widgets per minute.
The rate of N = y/5 widgets per minute.

The question basically asks whether x/4 > y/5 (if per minute M produces more widgets than N, then M obviously produces more widgets than N, in 20, 30, ... or in any time period. So, we can compare the rates per 1 minute).

(1) x > 0.8y --> x > 4/5*y --> x/4 > y/5. Sufficient.

(2) y = x + 1. The question becomes: is x/4 > (x+1)/5, or is x>4. We don't know that. Not sufficient.

Hope it's clear.

Hi Banuel: Is the following reasoning correct/possible to identify statement (2) as sufficient? Reasoning as follows:

Because we know x > 4, it must be at least 5 assuming you can't have a fraction of a widget (i.e. you can't produce 4.5 widgets every 4 minutes). Given that y = x + 1 which yields 6 in this case, then 5/4 > 6/5 is in fact true. Furthermore, this inequality stays true as the value of x increases. Thus, the statement could be sufficient?

That's circular reasoning. The question we are trying to answer is if $$\frac{x}{4}>\frac{y}{5}$$ and so it cannot be combined with a true statement. I would like to add that, if $$x=2$$ and $$y=3$$, then machine M produces 10 widgets and machine N produces 12 widgets, and therefore, machine M can produce less widgets per 20 minutes than machine N does.

Kr,
Mejia
Intern
Joined: 10 Oct 2015
Posts: 1
Followers: 0

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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

07 Jan 2016, 08:36
Hi Bunuel,

So basically we are comparing x/4 to 0.8y/4(keeping base same as 4). In second choice, y=x+1. so hence we are now trying to check if x>0.8(x+1) or 0.8x+0.8 I assumed that that 0.8y has to be an integer. Is this assumption correct. I took this assumption and arrived at that x>=0.8x+0.8 for any value where 0.8x+0.8 is an integer. Hence 2 is insufficient. Please tell me if this approach is Ok
GMAT Club Legend
Joined: 09 Sep 2013
Posts: 13423
Followers: 575

Kudos [?]: 163 [0], given: 0

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]

### Show Tags

12 Jan 2017, 14:49
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.
_________________
Re: Machine M, working alone at its constant rate, produces x wi   [#permalink] 12 Jan 2017, 14:49
Similar topics Replies Last post
Similar
Topics:
7 If machine J, working alone at its constant rate, takes 2 minutes to 6 25 Oct 2014, 03:14
29 Machine M and Machine N working alone at their constant rate 10 26 Jul 2014, 09:07
63 A newer machine, working alone at its constant rate 27 26 Oct 2013, 13:42
98 Machines X and Y work at their respective constant rates 19 23 Feb 2012, 08:05
12 Machines X and Y produced identical bottles at different constant rate 5 08 Nov 2011, 19:21
Display posts from previous: Sort by

# Machine M, working alone at its constant rate, produces x wi

 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®.