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

2

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6

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00:00

A

B

C

D

E

Difficulty:

65% (hard)

Question Stats:

55% (02:28) correct
45% (01:23) wrong based on 318 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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
25 Sep 2013, 01:40

10

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Expert's post

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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.

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

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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
03 Mar 2014, 00:43

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.

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
28 Mar 2015, 11:17

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Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
29 Mar 2015, 17:50

Expert's post

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

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

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.

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

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

Re: Machine M, working alone at its constant rate, produces x wi [#permalink]
06 May 2015, 19:45

Expert's post

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. _________________

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