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

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Machine M, working alone at its constant rate, produces x wi [#permalink] New post 24 Sep 2013, 07:29
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Question Stats:

55% (02:19) correct 45% (01:23) wrong based on 203 sessions
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 ?
[Reveal] Spoiler: OA
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Re: Machine M and Machine N [#permalink] New post 24 Sep 2013, 07:46
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
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Re: Machine M, working alone at its constant rate, produces x wi [#permalink] New post 25 Sep 2013, 01:40
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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.
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Re: Machine M, working alone at its constant rate, produces x wi [#permalink] New post 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.

Answer: A.

Hope it's clear.



Bunuel,

I am not able to understand statement B. Can you please elaborate...
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Re: Machine M, working alone at its constant rate, produces x wi [#permalink] New post 03 Mar 2014, 00:43
Expert's post
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.
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RESOURCES: [GMAT MATH BOOK]; 1. Triangles; 2. Polygons; 3. Coordinate Geometry; 4. Factorials; 5. Circles; 6. Number Theory; 7. Remainders; 8. Overlapping Sets; 9. PDF of Math Book; 10. Remainders; 11. GMAT Prep Software Analysis NEW!!!; 12. SEVEN SAMURAI OF 2012 (BEST DISCUSSIONS) NEW!!!; 12. Tricky questions from previous years. NEW!!!;

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.


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Re: Machine M, working alone at its constant rate, produces x wi [#permalink] New post 03 Mar 2014, 20:26
Expert's post
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
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Re: Machine M, working alone at its constant rate, produces x wi   [#permalink] 03 Mar 2014, 20:26
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