Author 
Message 
TAGS:

Hide Tags

Senior Manager
Joined: 22 Dec 2009
Posts: 324

Is integer x prime? [#permalink]
Show Tags
Updated on: 07 Jan 2014, 07:13
Question Stats:
82% (01:03) correct 18% (01:24) wrong based on 104 sessions
HideShow timer Statistics
Is integer x prime? (1) \(x^23\) is an even number (2) \(x+2\) is an odd number
Official Answer and Stats are available only to registered users. Register/ Login.
_________________
Cheers! JT........... If u like my post..... payback in Kudos!!
Do not post questions with OAPlease underline your SC questions while postingTry posting the explanation along with your answer choice For CR refer Powerscore CR BibleFor SC refer Manhattan SC Guide
~~Better Burn Out... Than Fade Away~~
Originally posted by jeeteshsingh on 07 Mar 2010, 10:23.
Last edited by Bunuel on 07 Jan 2014, 07:13, edited 3 times in total.
Edited the question and added the OA.



Senior Manager
Joined: 30 Aug 2009
Posts: 276
Location: India
Concentration: General Management

Re: Is integer x prime? [#permalink]
Show Tags
07 Mar 2010, 11:08
jeeteshsingh wrote: kp1811 wrote: jeeteshsingh wrote: Is Integer x prime? 1. \(x^23\) is an even number 2. \(x+2\) is an odd number
Please explain 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: 324

Re: Is integer x prime? [#permalink]
Show Tags
07 Mar 2010, 11:26
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 OAPlease underline your SC questions while postingTry posting the explanation along with your answer choice For CR refer Powerscore CR BibleFor SC refer Manhattan SC Guide
~~Better Burn Out... Than Fade Away~~



Senior Manager
Joined: 30 Aug 2009
Posts: 276
Location: India
Concentration: General Management

Re: Is integer x prime? [#permalink]
Show Tags
07 Mar 2010, 11:34
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: 324

Re: Is integer x prime? [#permalink]
Show Tags
07 Mar 2010, 11:39
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 OAPlease underline your SC questions while postingTry posting the explanation along with your answer choice For CR refer Powerscore CR BibleFor SC refer Manhattan SC Guide
~~Better Burn Out... Than Fade Away~~



SVP
Joined: 06 Sep 2013
Posts: 1883
Concentration: Finance

Re: Is Integer x prime? 1. x^23 is an even number 2. x+2 is an [#permalink]
Show Tags
07 Jan 2014, 07:04
jeeteshsingh wrote: Is Integer x prime? 1. \(x^23\) is an even number 2. \(x+2\) is an odd number
Please explain Yeah answer is clearly A cause in B, 1 is obviously not a prime number Now question, when they say that something is an odd number Do they mean odd integer? Cause I'm pretty sure the definitions of number and integer are different Now, can a decimal be odd? Say like 1.5 is odd and 1.2 is even I guess so right? Just wanted to clarify on those Cheers! J



Math Expert
Joined: 02 Sep 2009
Posts: 46207

Re: Is Integer x prime? 1. x^23 is an even number 2. x+2 is an [#permalink]
Show Tags
07 Jan 2014, 07:08



Math Expert
Joined: 02 Sep 2009
Posts: 46207

Re: Is Integer x prime? 1. x^23 is an even number 2. x+2 is an [#permalink]
Show Tags
07 Jan 2014, 07:12



Current Student
Joined: 10 Oct 2013
Posts: 33
Concentration: Marketing, Entrepreneurship

Re: Is integer x prime? [#permalink]
Show Tags
08 Jan 2014, 00:16
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! Hello, Just a small thing You say "x = sqrt(2m + 3) where m is >= 0 as you cannot have  ve sqrt." but your m can be 1, still square root would be +ve i.e 1; now you have to add x=1 to your list :1,3,5,7 etc. As 1 is not prime. A becomes insufficient. Cheers!!!



Manager
Joined: 20 Dec 2013
Posts: 123

Re: Is integer x prime? [#permalink]
Show Tags
08 Jan 2014, 00:30
jeeteshsingh wrote: Is integer x prime?
(1) \(x^23\) is an even number
(2) \(x+2\) is an odd number X is an integer. Statement I is insufficient: x = 5 (Prime) x = 9 (Not Prime) Statement II is insufficient: 5 + 2 is odd 9 + 2 is odd No need to combine since we are using the same set of numbers to disprove each statement individually Hence answer is E
_________________
76000 Subscribers, 7 million minutes of learning delivered and 5.6 million video views
Perfect Scores http://perfectscores.org http://www.youtube.com/perfectscores



Manager
Joined: 25 Oct 2013
Posts: 160

Re: Is integer x prime? [#permalink]
Show Tags
02 Feb 2014, 03:16
Stmt 1: \(x^23\) is even simply means x is odd integer. Now x being odd is not sufficient for it to be prime. INSUFF Stm2: x+2 is odd means x is odd integer. Therefore stmt 1 & 2 are same. INSUFF Both statements together give no new information. hence E.
_________________
Click on Kudos if you liked the post!
Practice makes Perfect.



NonHuman User
Joined: 09 Sep 2013
Posts: 7009

Re: Is integer x prime? [#permalink]
Show Tags
24 Jan 2018, 04:34
Hello from the GMAT Club BumpBot! Thanks to another GMAT Club member, I have just discovered this valuable topic, yet it had no discussion for over a year. I am now bumping it up  doing my job. I think you may find it valuable (esp those replies with Kudos). Want to see all other topics I dig out? Follow me (click follow button on profile). You will receive a summary of all topics I bump in your profile area as well as via email.
_________________
GMAT Books  GMAT Club Tests  Best Prices on GMAT Courses  GMAT Mobile App  Math Resources  Verbal Resources




Re: Is integer x prime?
[#permalink]
24 Jan 2018, 04:34






