Find all School-related info fast with the new School-Specific MBA Forum

 It is currently 18 Dec 2013, 00:00

# Events & Promotions

###### Events & Promotions in June
Open Detailed Calendar

# Is Integer x prime? 1. x^2-3 is an even number 2. x+2 is an

 Question banks Downloads My Bookmarks Reviews Important topics
Author Message
TAGS:
Senior Manager
Joined: 22 Dec 2009
Posts: 366
Followers: 9

Kudos [?]: 167 [0], given: 47

Is Integer x prime? 1. x^2-3 is an even number 2. x+2 is an [#permalink]  07 Mar 2010, 09:23
00:00

Difficulty:

5% (low)

Question Stats:

100% (02:33) correct 0% (00:00) wrong based on 6 sessions
Is Integer x prime?
1. x^2-3 is an even number
2. x+2 is an odd number

_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice|
|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

Last edited by jeeteshsingh on 07 Mar 2010, 10:01, edited 1 time in total.
Senior Manager
Joined: 22 Dec 2009
Posts: 366
Followers: 9

Kudos [?]: 167 [0], given: 47

Re: Is integer x prime? [#permalink]  07 Mar 2010, 10:02
kp1811 wrote:
jeeteshsingh wrote:
Is Integer x prime?
1. x^2-3 is an even number
2. x+2 is an odd number

E...

Made the question more clear for you...!
_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice|
|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

Senior Manager
Joined: 30 Aug 2009
Posts: 293
Location: India
Concentration: General Management
Followers: 2

Kudos [?]: 75 [0], given: 5

Re: Is integer x prime? [#permalink]  07 Mar 2010, 10:08
jeeteshsingh wrote:
kp1811 wrote:
jeeteshsingh wrote:
Is Integer x prime?
1. x^2-3 is an even number
2. x+2 is an odd number

E...

Made the question more clear for you...!

will try to make it more clearer.....

stmnt1) x^2 - 3 is even

let x = 3 (prime) then 3^2 - 3 = 6 even
let x =9 (non prime) then 9^2 - 3 = 78 even
hence insuff

stmnt2) x+2 is odd
let x = 3 (prime) then 3 + 2 = 5 odd
let x =9 (non prime) then 9 + 2 = 11 odd
hence insuff

even together they don't suffice. Hence E
Senior Manager
Joined: 22 Dec 2009
Posts: 366
Followers: 9

Kudos [?]: 167 [0], given: 47

Re: Is integer x prime? [#permalink]  07 Mar 2010, 10:26
kp1811 wrote:
jeeteshsingh wrote:

will try to make it more clearer.....

stmnt1) x^2 - 3 is even

let x = 3 (prime) then 3^2 - 3 = 6 even
let x =9 (non prime) then 9^2 - 3 = 78 even
hence insuff

stmnt2) x+2 is odd
let x = 3 (prime) then 3 + 2 = 5 odd
let x =9 (non prime) then 9 + 2 = 11 odd
hence insuff

even together they don't suffice. Hence E

Some how I dont get this approach as you use the ques to prove the statement below. This question is from PR 1012 and I see the same solution there which isnt convincing for me.

My approach is as follows:

Given x is an integer.
Ques is x prime?

S1: x^2 - 3 = even
x^2 - 3 = 2m where m is an integer
x = sqrt(2m + 3) where m is >= 0 as you cannot have - ve sqrt.

This gives x = \sqrt{3},\sqrt{5},\sqrt{7},3,\sqrt{11},\sqrt{13},\sqrt{15},\sqrt{17},\sqrt{19},\sqrt{21},\sqrt{23},5,\sqrt{27},\sqrt{29},.....
Since it is given that x is an integer we get only 3, 5, 7..... which are all prime. Hence SUFF.

S2: x + 2 is odd
x + 2 = 2k + 1 where k is an integer
x = 2k - 1
Therefore x = ....-7,-5,-3,-1,1,3,5,7,9,11... which means all odd numbers and hence not necessarily be prime. Therefore NOT SUFF.

Hence answer is A....!

Can someone highlight what is wrong in my approach!
_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice|
|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

Senior Manager
Joined: 30 Aug 2009
Posts: 293
Location: India
Concentration: General Management
Followers: 2

Kudos [?]: 75 [1] , given: 5

Re: Is integer x prime? [#permalink]  07 Mar 2010, 10:34
1
KUDOS
jeeteshsingh wrote:
kp1811 wrote:
jeeteshsingh wrote:

will try to make it more clearer.....

stmnt1) x^2 - 3 is even

let x = 3 (prime) then 3^2 - 3 = 6 even
let x =9 (non prime) then 9^2 - 3 = 78 even
hence insuff

stmnt2) x+2 is odd
let x = 3 (prime) then 3 + 2 = 5 odd
let x =9 (non prime) then 9 + 2 = 11 odd
hence insuff

even together they don't suffice. Hence E

Some how I dont get this approach as you use the ques to prove the statement below. This question is from PR 1012 and I see the same solution there which isnt convincing for me.

My approach is as follows:

Given x is an integer.
Ques is x prime?

S1: x^2 - 3 = even
x^2 - 3 = 2m where m is an integer
x = sqrt(2m + 3) where m is >= 0 as you cannot have - ve sqrt.

This gives x = \sqrt{3},\sqrt{5},\sqrt{7},3,\sqrt{11},\sqrt{13},\sqrt{15},\sqrt{17},\sqrt{19},\sqrt{21},\sqrt{23},5,\sqrt{27},\sqrt{29},.....
Since it is given that x is an integer we get only 3, 5, 7..... which are all prime. Hence SUFF.

S2: x + 2 is odd
x + 2 = 2k + 1 where k is an integer
x = 2k - 1
Therefore x = ....-7,-5,-3,-1,1,3,5,7,9,11... which means all odd numbers and hence not necessarily be prime. Therefore NOT SUFF.

Hence answer is A....!

Can someone highlight what is wrong in my approach!

in highlighted part after 3,5, 7 .... 9 will come [ for m = 39] which is non prime
Senior Manager
Joined: 22 Dec 2009
Posts: 366
Followers: 9

Kudos [?]: 167 [0], given: 47

Re: Is integer x prime? [#permalink]  07 Mar 2010, 10:39
kp1811 wrote:
jeeteshsingh wrote:

Some how I dont get this approach as you use the ques to prove the statement below. This question is from PR 1012 and I see the same solution there which isnt convincing for me.

My approach is as follows:

Given x is an integer.
Ques is x prime?

S1: x^2 - 3 = even
x^2 - 3 = 2m where m is an integer
x = sqrt(2m + 3) where m is >= 0 as you cannot have - ve sqrt.

This gives x = \sqrt{3},\sqrt{5},\sqrt{7},3,\sqrt{11},\sqrt{13},\sqrt{15},\sqrt{17},\sqrt{19},\sqrt{21},\sqrt{23},5,\sqrt{27},\sqrt{29},.....
Since it is given that x is an integer we get only 3, 5, 7..... which are all prime. Hence SUFF.

S2: x + 2 is odd
x + 2 = 2k + 1 where k is an integer
x = 2k - 1
Therefore x = ....-7,-5,-3,-1,1,3,5,7,9,11... which means all odd numbers and hence not necessarily be prime. Therefore NOT SUFF.

Hence answer is A....!

Can someone highlight what is wrong in my approach!

in highlighted part after 3,5, 7 .... 9 will come [ for m = 39] which is non prime

Thanks mate! Got it Now! Kudos +1
_________________

Cheers!
JT...........
If u like my post..... payback in Kudos!!

|Do not post questions with OA|Please underline your SC questions while posting|Try posting the explanation along with your answer choice|
|For CR refer Powerscore CR Bible|For SC refer Manhattan SC Guide|

~~Better Burn Out... Than Fade Away~~

Re: Is integer x prime?   [#permalink] 07 Mar 2010, 10:39
Similar topics Replies Last post
Similar
Topics:
Is the odd integer X a prime number? 1) X+2 is a prime 5 02 Jul 2004, 08:51
If x is an integer , is (x^2+1)(x^2+5) an even number? (1) x 6 02 Jan 2009, 20:41
1 if x is an integer, is (x^2 + 1) (x + 5) an even number? (1) 3 23 Apr 2011, 14:54
If x is an integer, is (x^2 +1) (x+5) an even number? 7 29 Jul 2011, 01:31
3 If x is an integer, is (x^2+1)(x+5) an even number? 3 28 Jan 2012, 04:56
Display posts from previous: Sort by

# Is Integer x prime? 1. x^2-3 is an even number 2. x+2 is an

 Question banks Downloads My Bookmarks Reviews Important topics

 Powered by phpBB © phpBB Group and phpBB SEO Kindly note that the GMAT® test is a registered trademark of the Graduate Management Admission Council®, and this site has neither been reviewed nor endorsed by GMAC®.