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Is the value of expression k – m + 1 greater than the

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Is the value of expression k – m + 1 greater than the [#permalink] New post 25 Oct 2012, 20:34
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Question Stats:

70% (01:45) correct 30% (00:57) wrong based on 63 sessions
Is the value of expression k – m + 1 greater than the expression k+ m – 1.

(1) k is greater than zero.

(2) m is less than zero.

So my train of thoughts were to simply this:

Is k - m + 1 > k + m - 1 ?

or

1 - m > m - 1

2 > 2m

Is m < 1 ?

Now the question is easier to answer.

Statement 1)

If k > 0, well it shouldn't matter what k is, so I thought this was okay, so I thought statement 1 is true.

Statement 2)

Clearly if m < 0, then m < 1. So statement 2) is true.

So I put down D as answer.

But for some reason, the answer choice is only statement 2) is true.

What's the explanation for that? Since in statement 1, it should not really matter a jot what k is?

Thanks as always for your help.

Best wishes.
[Reveal] Spoiler: OA

Last edited by Bunuel on 26 Oct 2012, 03:29, edited 1 time in total.
Renamed the topic and edited the question.
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Re: Simplifying algebra question [#permalink] New post 25 Oct 2012, 21:10
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elegan wrote:
Hello,

The question is:

Is the value of expression k – m + 1 greater than the expression k+ m – 1.
(1) k is greater than zero.
(2) m is less than zero.

So my train of thoughts were to simply this:

Is k - m + 1 > k + m - 1 ?
or
1 - m > m - 1
2 > 2m
Is m < 1 ?

Now the question is easier to answer.

Statement 1)
If k > 0, well it shouldn't matter what k is, so I thought this was okay, so I thought statement 1 is true.

Statement 2)
Clearly if m < 0, then m < 1. So statement 2) is true.

So I put down D as answer.

But for some reason, the answer choice is only statement 2) is true.
What's the explanation for that? Since in statement 1, it should not really matter a jot what k is?
Thanks as always for your help.
Best wishes.


You've done everything correctly till you've simplified question to
is m < 1 ?

from here, when analyzing statement 1 you made the mistake.

think about it logically. if k >0 or K <0 or K is anything in the world, can it help to find out what m would be? nope.
K can be 50, m could be 5
or K can be 100 and m could be -5
therefore it is not sufficient to tell if m<1 or m>1

statement ii however talks about m. and says m<0 if m <0 and we know 0<1 that would mean m<1 -
With this statement we can say 'yes' m is less than 1

So ans is B.

Hope it helps
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Re: Simplifying algebra question [#permalink] New post 25 Oct 2012, 22:32
elegan wrote:
Hello,

The question is:

Is the value of expression k – m + 1 greater than the expression k+ m – 1.

(1) k is greater than zero.

(2) m is less than zero.

So my train of thoughts were to simply this:

Is k - m + 1 > k + m - 1 ?

or

1 - m > m - 1

2 > 2m

Is m < 1 ?

Now the question is easier to answer.

Statement 1)

If k > 0, well it shouldn't matter what k is,

There. You have answered your question yourself. The question asks for whether the data is sufficient i.e whether it matters.

so I thought this was okay, so I thought statement 1 is true.

Statement 2)

Clearly if m < 0, then m < 1. So statement 2) is true.

So I put down D as answer.

But for some reason, the answer choice is only statement 2) is true.

What's the explanation for that? Since in statement 1, it should not really matter a jot what k is?

Thanks as always for your help.

Best wishes.



Since as you said, IT does not matter. A and D can be elminated as wrong answer choices.

Kudos Please... If my post helped.
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Re: Is the value of expression k – m + 1 greater than the [#permalink] New post 26 Oct 2012, 03:45
if u dont care what K is?? then how can it be sufficient..??

K cud b anything..greater than 0 or less than 0..

hope it helps..
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Re: Is the value of expression k – m + 1 greater than the [#permalink] New post 26 Oct 2012, 13:26
Expert's post
elegan wrote:
Statement 1)

If k > 0, well it shouldn't matter what k is, so I thought this was okay, so I thought statement 1 is true.

Dear elegan,

Everyone else on the page said that you were wrong, but it's not clear to me that anyone explained in clearly enough so that you now fully understand the deeper issue at play here.

I'll begin by saying, here are a couple blogs you may find informative about DS in general.
http://magoosh.com/gmat/2012/introducti ... fficiency/
http://magoosh.com/gmat/2012/gmat-data- ... trategies/

You made a very classic DS mistake ---- confusing the "truth value question" with the "sufficiency question."

The prompt in this question is: "Is the value of expression k – m + 1 greater than the expression k+ m – 1?" That's a 'truth value question", about whether a mathematical statement is true or false. Technically speaking, we are not answering this question at all. Technically, our job on DS is to answer the "sufficiency question" --- viz., given this new piece of information, the DS Statement, would this piece of information allow me to determine a definitive answer to the prompt question?

When you look at a DS statement, your job is not to answer any of these questions
"is this true?"
"could this be true?"
"would it be OK if this were true?"
"is this consistent with the prompt?"
Rather, your job is very focused and specific: your job is to answer the single question
"Is this statement sufficient?"
i.e.
"If I were given this statement as a true piece of information, over and above whatever true pieces of info I have from the prompt, does this allow me to determine a definitive answer to the prompt question?"
All of math depends on precision. In DS, part of success is making sure that you are always answering the sufficiency question, and never any other question, when you evaluate these statements.

If you are considering a different question than the one you are supposed to consider, you will tend to get DS questions incorrect. For example, in this case, recognizing the value of K doesn't matter would lead to a resounding "yes!" if we were working with something like the question "could this be true?", but if we are working very strictly with the sufficiency question, irrelevance generally does not help us at all in determining anything definitively. If we focus precisely on the sufficiency question, we must arrive at a "no" answer here ---- statement #1 is not sufficient.

Does all this make sense?

Mike :-)
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Re: Is the value of expression k – m + 1 greater than the   [#permalink] 26 Oct 2012, 13:26
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