Author 
Message 
Intern
Joined: 15 Feb 2009
Posts: 12

If X is a prime number, what's the value of X? (1) X < 15 [#permalink]
Show Tags
12 Jun 2009, 17:52
Question Stats:
0% (00:00) correct 0% (00:00) wrong based on 0 sessions
HideShow timer Statistics
If X is a prime number, what's the value of X? (1) X < 15 (2) (X2) is a multiple of 5. The correct answer is E....why? I think it's C and here's how I solved it from (1), X can be 2,3,5,7,11 and 13 from (2) X is 7 because 7  2 = 5 which is a multiple of 5 == Message from GMAT Club Team == This is not a quality discussion. It has been retired. If you would like to discuss this question please repost it in the respective forum. Thank you! To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative  Verbal Please note  we may remove posts that do not follow our posting guidelines. Thank you.



Manager
Joined: 11 Apr 2009
Posts: 157

Re: prime numbers  DS [#permalink]
Show Tags
12 Jun 2009, 21:19
The answer can be E here:
1 is not sufficient. 2 is not sufficient either.
Together take values of X as 2, then 22 = 0 , which is a multiple of 5 (as 0*5=0). (0 is a multiple of 5). X=7 will also give a multiple of 5.
Thus E.



Intern
Joined: 08 Jun 2009
Posts: 32

Re: prime numbers  DS [#permalink]
Show Tags
12 Jun 2009, 21:22
Hi,
It is because there can be many values of x that fulfills the second statement.
For example: 172 = 15, multiple of 5 too.
We do not know whether X is 15 or 5, hence insufficient.



Manager
Joined: 12 Apr 2006
Posts: 210
Location: India

Re: prime numbers  DS [#permalink]
Show Tags
12 Jun 2009, 21:28
MontrealGirl wrote: If X is a prime number, what's the value of X?
(1) X < 15 (2) (X2) is a multiple of 5.
The correct answer is E....why?
I think it's C and here's how I solved it
from (1), X can be 2,3,5,7,11 and 13 from (2) X can be 17, 37, and similar.
Combining both X is 7 because 7  2 = 5 which is a multiple of 5 You are right I got to the same conclusion. What is the source of this question and OE. Or may be they are not considering 5 as multiple of 5.



Manager
Joined: 11 Apr 2009
Posts: 157

Re: prime numbers  DS [#permalink]
Show Tags
12 Jun 2009, 21:30
X cannot be 17 because X<15. Hence the values possible for X are 2 and 7 (prime nos) where X2 is a multiple of 5.



Manager
Joined: 12 Apr 2006
Posts: 210
Location: India

Re: prime numbers  DS [#permalink]
Show Tags
12 Jun 2009, 21:31
gmatprep09 wrote: The answer can be E here:
1 is not sufficient. 2 is not sufficient either.
Together take values of X as 2, then 22 = 0 , which is a multiple of 5 (as 0*5=0). (0 is a multiple of 5). X=7 will also give a multiple of 5.
Thus E. Not sure but seems the only plausible explanation. Thanks



Intern
Joined: 15 Feb 2009
Posts: 12

Re: prime numbers  DS [#permalink]
Show Tags
13 Jun 2009, 06:54
Jozu wrote: Hi,
It is because there can be many values of x that fulfills the second statement.
For example: 172 = 15, multiple of 5 too.
We do not know whether X is 15 or 5, hence insufficient. but from (1), we know that the prime number should be less than 15



Intern
Joined: 15 Feb 2009
Posts: 12

Re: prime numbers  DS [#permalink]
Show Tags
13 Jun 2009, 06:54
humans wrote: MontrealGirl wrote: If X is a prime number, what's the value of X?
(1) X < 15 (2) (X2) is a multiple of 5.
The correct answer is E....why?
I think it's C and here's how I solved it
from (1), X can be 2,3,5,7,11 and 13 from (2) X can be 17, 37, and similar.
Combining both X is 7 because 7  2 = 5 which is a multiple of 5 You are right I got to the same conclusion. What is the source of this question and OE. Or may be they are not considering 5 as multiple of 5. Kaplan practice test



Retired Moderator
Joined: 05 Jul 2006
Posts: 1741

Re: prime numbers  DS [#permalink]
Show Tags
16 Jun 2009, 14:16
[quote="MontrealGirl"]If X is a prime number, what's the value of X?
(1) X < 15 (2) (X2) is a multiple of 5.
obviously each alone is not suff
both
x2 = 5a
x = 5a2.. x = 3 or13,23.....etc
from one x<15 ie x = 2or3,5,7,11,13
the intersection of the 2 one and two is 3,13 we cant determine one single value...thus E



SVP
Joined: 29 Aug 2007
Posts: 2453

Re: prime numbers  DS [#permalink]
Show Tags
17 Jun 2009, 18:36
yezz wrote: MontrealGirl wrote: If X is a prime number, what's the value of X?
(1) X < 15 (2) (X2) is a multiple of 5.
obviously each alone is not suff
both
x2 = 5a
x = 5a2.. x = 3 or13,23.....etc
from one x<15 ie x = 2or3,5,7,11,13
the intersection of the 2 one and two is 3,13 we cant determine one single value...thus E A small correction note for a typo: x = 5a + 2.. x = 2 or 7 or 12 or 17 or so on....
_________________
Verbal: http://gmatclub.com/forum/newtotheverbalforumpleasereadthisfirst77546.html Math: http://gmatclub.com/forum/newtothemathforumpleasereadthisfirst77764.html Gmat: http://gmatclub.com/forum/everythingyouneedtoprepareforthegmatrevised77983.html
GT



VP
Joined: 05 Jul 2008
Posts: 1373

Re: prime numbers  DS [#permalink]
Show Tags
18 Jun 2009, 08:59
gmatprep09 wrote: The answer can be E here:
1 is not sufficient. 2 is not sufficient either.
Together take values of X as 2, then 22 = 0 , which is a multiple of 5 (as 0*5=0). (0 is a multiple of 5). X=7 will also give a multiple of 5.
Thus E. Leaving out zero is the reason why we will get C. == Message from GMAT Club Team == This is not a quality discussion. It has been retired. If you would like to discuss this question please repost it in the respective forum. Thank you! To review the GMAT Club's Forums Posting Guidelines, please follow these links: Quantitative  Verbal Please note  we may remove posts that do not follow our posting guidelines. Thank you.




Re: prime numbers  DS
[#permalink]
18 Jun 2009, 08:59






