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M08: q36

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Manager
Joined: 16 Feb 2010
Posts: 218

Kudos [?]: 377 [0], given: 16

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11 Nov 2010, 11:35
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.

-1+2 =1 which is prime, therefore C should be the correct anser - please amend.....thanks

Kudos [?]: 377 [0], given: 16

Manager
Joined: 29 Oct 2009
Posts: 196

Kudos [?]: 111 [0], given: 12

Concentration: General Management, Sustainability
WE: Consulting (Computer Software)

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12 Nov 2010, 10:46
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.

hope this helps.
_________________

+1Kudos, if this helps

Kudos [?]: 111 [0], given: 12

Manager
Joined: 16 Feb 2010
Posts: 218

Kudos [?]: 377 [0], given: 16

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13 Nov 2010, 03:03
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.

hope this helps.

yes - i agree. who should i contact to change the OA on the test?

Kudos [?]: 377 [0], given: 16

Re: M08: q36   [#permalink] 13 Nov 2010, 03:03
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M08: q36

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