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H_to_750
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Post subject: Is X between 0 and 1  Posted: Sat Mar 01, 2008 7:41 pm |
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Source:- Manhattan Lab # 2 - Data sufficency - Yes / No testing LAB
Question Number 206. I belive this is an OG number.
Question:-
[question deleted because it is an OG question]
Statement 1 is in Insufficient because we don’t know if x is a positive or negative. If x is positive fraction ½ than statement one is sufficient but if x is negative – ½ than it will not work because when squared it will return a positive answer. Statement Insufficient
Statement two is insufficient because we don’t know what is the value of x it can be a fraction or not a fraction.
When we combine both statements we know from statement two that x is positive and statement one tells us it is a fraction. Sufficient. I think “C” is the correct answer.
On the LAB correct answer was marked as “A”. Can someone explain.
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blue_lotus
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Post subject: Posted: Sun Mar 02, 2008 7:40 pm |
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Using 1:
x^2 is less than x
try using different values and find which value of x does satisfy the above given condition
-> if x is negative for example -1 , X^2 = 1 which is greater than X, so it does not satisfy
-> if x is positive greater than 1, let x =2 , X^2 =4 , still greater
-> if x = 0 , X^2 = 0, still not less than X.
-> if x is between 0 and 1, if x = 1/2 , x^2 = 1/4, which is less
the conclusion is is x is between 0 and 1, SUFFICIENT
Note: properties like this has to be remembered to save time in actual GMAT.
Using 2: X^3 is positive,
this only means X is +ve and does not give any range
ANS therefore is A
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H_to_750
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Post subject: what if x is -1/2 Posted: Sun Mar 02, 2008 9:22 pm |
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thank you blue_lotus for your reply
But if x is -1/2 it will still yeild positive 1/4.
than x can be positive 1/2 or negative -1/2 and in both than for statement one answer is may be.
What am i missing here?
thanks in advance
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tmmyc
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Post subject: Posted: Mon Mar 03, 2008 12:18 am |
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If x is -1/2, then x^2 is 1/4.
1/4 > -1/2 so
x^2 > x
However, Statement 1 states x^2 < x
Therefore -1/2 is not a valid value for x in this case.
As blue_lotus showed, only positive fractions meet the criteria for Statement 1 and therefore can sufficiently answer the question if x is between 0 and 1.
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blue_lotus
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Post subject: Posted: Mon Mar 03, 2008 4:21 am |
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tmmyc is right, -1/2 does not meet the mentioned criterial .
Any negative number will not meet the criteria as
square of any negative number whether it is an integer or fraction,it will be positive, and postive number is always greater than negative number.
so we can conclude that the number range we are looking for is not less than 0. i.e x > 0
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H_to_750
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Post subject: Posted: Mon Mar 03, 2008 10:28 am |
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Ah Haa
Thanks allot guys.
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StaceyKoprince
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Post subject: Posted: Wed Mar 12, 2008 5:59 pm |
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