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M08: q36

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Manager
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Joined: 16 Feb 2010
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M08: q36 [#permalink] New post 11 Nov 2010, 10:35
What is X ?

1. X^2 - 1 = X + 1
2. X + 3 is a prime number

(C) 2008 GMAT Club - m08#36

* Statement (1) ALONE is sufficient, but Statement (2) ALONE is not sufficient
* Statement (2) ALONE is sufficient, but Statement (1) ALONE is not sufficient
* BOTH statements TOGETHER are sufficient, but NEITHER statement ALONE is sufficient
* EACH statement ALONE is sufficient
* Statements (1) and (2) TOGETHER are NOT sufficient

Statement (1) by itself is insufficient. From S1, X is either 2 or -1. Be careful not to cancel out the factor (X + 1) for it can equal 0.

Statement (2) by itself is insufficient. S2 does not help to determine whether X is -1 or 2 as both 2 and 5 are primes.
The correct answer is E.


-1+2 =1 which is prime, therefore C should be the correct anser - please amend.....thanks
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Manager
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Joined: 29 Oct 2009
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Concentration: General Management, Sustainability
WE: Consulting (Computer Software)
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Re: M08: q36 [#permalink] New post 12 Nov 2010, 09:46
The correct answer is E.
Here is the explanation.
Statement 1:
x^2-1 = x +1
x^2-1-x-1 = 0
x^2-x-2 = 0
(x-2) (x+1) = 0
Here x is either 2 or -1. Not sufficient.

Statement 3: X+3 is prime number. X xould be any number like 2,4,8...etc. So Not sufficient.

Together: If we consider statement 1 and 2 togather.
x=2 , X+3 = 5 is prime -- True
x=-1, x+3 = -1+3 = 2 is prime --True.

Again we get two solutions for x (2 or -1). Which is insuffient to find x.

So the answer is E.

hope this helps.
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+1Kudos, if this helps

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Re: M08: q36 [#permalink] New post 13 Nov 2010, 02:03
mads wrote:
The correct answer is E.
Here is the explanation.
Statement 1:
x^2-1 = x +1
x^2-1-x-1 = 0
x^2-x-2 = 0
(x-2) (x+1) = 0
Here x is either 2 or -1. Not sufficient.

Statement 3: X+3 is prime number. X xould be any number like 2,4,8...etc. So Not sufficient.

Together: If we consider statement 1 and 2 togather.
x=2 , X+3 = 5 is prime -- True
x=-1, x+3 = -1+3 = 2 is prime --True.

Again we get two solutions for x (2 or -1). Which is insuffient to find x.

So the answer is E.

hope this helps.


yes - i agree. who should i contact to change the OA on the test?
Re: M08: q36   [#permalink] 13 Nov 2010, 02:03
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M08: q36

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