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GMATPrep Question pack 1 doubt

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by xyzx5230 » Thu Aug 01, 2013 1:42 am
I have attached the screen shot of a question. I am not sure how option III is correct. GMATPrep solution is also given here. It says, Since X<-3 implies X<-1. But putting X=-2 in Mod will not hold given condition (mod X > 3) true.
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Source: — Problem Solving |

by GMATGuruNY » Thu Aug 01, 2013 3:08 am
|a| = the distance between a and 0.
|a-b| = the distance between a and b.
IF |X|>3, which of the following must be true?
A) X>3
B) X^2>9
c) |X-1|>2
I only
II only
I and II only
II and III only
I, II, and III
Constraint: |x| > 3
This means that the distance between x and 0 is greater than 3.
Any value in the two red ranges below satisfies this constraint:
<----(-3).......(3)---->

I: x>3
The red range on the left illustrates that x does not have to be greater than 3.
Eliminate A, C, and E.

III: |x-1| > 2.
This statement implies that the distance between x and 1 must be greater than 2.
Every value in the red ranges above is more than 2 places away from 1.
Thus, statement III must be true.
Eliminate B.

The correct answer is D.
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by [email protected] » Thu Aug 01, 2013 5:10 pm
Hi xyzx5230,

You made a slight logical mistake on this question: You didn't follow the instructions.

The first piece of information tells you that |X| > 3, so the value of X can be > 3 OR the value of X can be < -3

Your choice to use X = -2 is not permissible in this question.

Mitch's explanation for the rest of the question is solid.

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by mgm » Thu Aug 01, 2013 5:48 pm
|x-1| > 2 ==> -x+1 > 2 ==> x < -1 ...so if x = -2 but this is not valid if x < -3 then the condition does not hold...
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by macattack » Fri Aug 02, 2013 3:45 am
c) |x-1| > 2 ==> 2 cases: x>3 or x<-1

Given |x|>3 we have x>3 or x<-3
as you can see in c) x>3 is satisfied and x<-1 is satisfied so the answer is correct.
x<-3 implies x<-1
I hope its clear now mgm. If you have further queries kindly advise and I wil be happy to help.
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by AmitPareek » Sat Aug 03, 2013 9:09 pm
In my view OA should be B. As it is the only condition satisfying lxl<3.
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by [email protected] » Sun Aug 04, 2013 10:18 am
Hi AmitPareek,

You have to very careful with Roman Numeral questions, as there can sometimes be patterns that you don't immediately notice. Roman Numeral II is only PART of the answer. With some experimentation (try TESTing numbers), you'll find that Roman Numeral III is ALSO true, so the final answer IS D.

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Rich
Contact Rich at [email protected]
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