Author 
Message 
TAGS:

Hide Tags

Intern
Joined: 24 Jan 2012
Posts: 9

Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
24 Sep 2013, 08:29
3
This post received KUDOS
28
This post was BOOKMARKED
Question Stats:
58% (02:23) correct
42% (01:29) wrong based on 882 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 ACan someone please explain ?
Official Answer and Stats are available only to registered users. Register/ Login.



Intern
Joined: 07 Aug 2013
Posts: 29

Re: Machine M and Machine N [#permalink]
Show Tags
24 Sep 2013, 08:46
1
This post received 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: 39673

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
25 Sep 2013, 02:40
33
This post received KUDOS
Expert's post
13
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. Answer: A. Hope it's clear.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Manager
Joined: 14 Jan 2013
Posts: 153
Concentration: Strategy, Technology
GMAT Date: 08012013
GPA: 3.7
WE: Consulting (Consulting)

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
03 Mar 2014, 01:40
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.
Answer: A.
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/collectionofarticlesoncriticalreasoning159959.html
http://gmatclub.com/forum/percentages700800levelquestions130588.html
http://gmatclub.com/forum/700to800levelquantquestionwithdetailsoluition143321.html



Math Expert
Joined: 02 Sep 2009
Posts: 39673

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
03 Mar 2014, 01:43
1
This post received 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.
Answer: A.
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.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



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)

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
03 Mar 2014, 21:26
1
This post received 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
_________________
MY GMAT BLOG  ADVICE  OPINIONS  ANALYSIS



GMAT Club Legend
Joined: 09 Sep 2013
Posts: 15980

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
28 Mar 2015, 12:17
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.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources



EMPOWERgmat Instructor
Status: GMAT Assassin/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 9271
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
29 Mar 2015, 18:50
2
This post received KUDOS
Expert's post
3
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 notetaking 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 Final Answer: GMAT assassins aren't born, they're made, Rich
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************



Manager
Joined: 08 Oct 2013
Posts: 52

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
05 May 2015, 10:39
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/CoFounder
Affiliations: EMPOWERgmat
Joined: 19 Dec 2014
Posts: 9271
Location: United States (CA)
GRE 1: 340 Q170 V170

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
06 May 2015, 11:31
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
_________________
760+: Learn What GMAT Assassins Do to Score at the Highest Levels Contact Rich at: Rich.C@empowergmat.com
Rich Cohen
CoFounder & GMAT Assassin
***********************Select EMPOWERgmat Courses now include ALL 6 Official GMAC CATs!***********************



Manager
Joined: 08 Oct 2013
Posts: 52

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
06 May 2015, 12:08
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: 7440
Location: Pune, India

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
06 May 2015, 20:45
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
Can someone please explain ? 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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
16 Aug 2015, 22:03
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.
Answer: A.
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: 39673

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
17 Aug 2015, 01:46
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.
Answer: A.
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.
_________________
New to the Math Forum? Please read this: All You Need for Quant  PLEASE READ AND FOLLOW: 12 Rules for Posting!!! Resources: GMAT Math Book  Triangles  Polygons  Coordinate Geometry  Factorials  Circles  Number Theory  Remainders; 8. Overlapping Sets  PDF of Math Book; 10. Remainders  GMAT Prep Software Analysis  SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS)  Tricky questions from previous years.
Collection of Questions: PS: 1. Tough and Tricky questions; 2. Hard questions; 3. Hard questions part 2; 4. Standard deviation; 5. Tough Problem Solving Questions With Solutions; 6. Probability and Combinations Questions With Solutions; 7 Tough and tricky exponents and roots questions; 8 12 Easy Pieces (or not?); 9 Bakers' Dozen; 10 Algebra set. ,11 Mixed Questions, 12 Fresh Meat DS: 1. DS tough questions; 2. DS tough questions part 2; 3. DS tough questions part 3; 4. DS Standard deviation; 5. Inequalities; 6. 700+ GMAT Data Sufficiency Questions With Explanations; 7 Tough and tricky exponents and roots questions; 8 The Discreet Charm of the DS; 9 Devil's Dozen!!!; 10 Number Properties set., 11 New DS set.
What are GMAT Club Tests? Extrahard Quant Tests with Brilliant Analytics



Senior Manager
Joined: 15 Sep 2011
Posts: 361
Location: United States
WE: Corporate Finance (Manufacturing)

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
19 Sep 2015, 12:44
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.
Answer: A.
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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
07 Jan 2016, 09:36
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: 15980

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
Show Tags
12 Jan 2017, 15:49
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.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: Machine M, working alone at its constant rate, produces x wi
[#permalink]
12 Jan 2017, 15:49







