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

It is currently 11 Jul 2014, 16:28

Close

GMAT Club Daily Prep

Thank you for using the timer - this advanced tool can estimate your performance and suggest more practice questions. We have subscribed you to Daily Prep Questions via email.

Customized
for You

we will pick new questions that match your level based on your Timer History

Track
Your Progress

every week, we’ll send you an estimated GMAT score based on your performance

Practice
Pays

we will pick new questions that match your level based on your Timer History

Not interested in getting valuable practice questions and articles delivered to your email? No problem, unsubscribe here.

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

ds#positive integer

  Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
TAGS:
SVP
SVP
User avatar
Joined: 28 May 2005
Posts: 1743
Location: Dhaka
Followers: 6

Kudos [?]: 27 [0], given: 0

GMAT Tests User
ds#positive integer [#permalink] New post 30 Sep 2005, 10:14
00:00
A
B
C
D
E

Difficulty:

  5% (low)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions
OA to be followed....
Attachments

ds_positive integer.JPG
ds_positive integer.JPG [ 13.57 KiB | Viewed 315 times ]


_________________

hey ya......

VP
VP
avatar
Joined: 22 Aug 2005
Posts: 1128
Location: CA
Followers: 1

Kudos [?]: 20 [0], given: 0

GMAT Tests User
 [#permalink] New post 30 Sep 2005, 11:08
C.
r = 0
here is partial explanation:

question stem:
(n-1) * (n+1) = r (mod 24) , 0 <= r < 24, or
n^2 - 1 = r (mod 24) or
24 / n^2 -1 -r where 0 <= r < 24

the only thing i remember is that any number of the form (n^2 - 1) is divisible by 24 if n is prime > 3.

(1) and (2) confirms that n is prime and is > 3

when 24/n^2-1, r will be 0

Last edited by duttsit on 30 Sep 2005, 12:30, edited 1 time in total.
Current Student
avatar
Joined: 28 Dec 2004
Posts: 3405
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 13

Kudos [?]: 149 [0], given: 2

GMAT Tests User
 [#permalink] New post 30 Sep 2005, 11:10
Ok lets see....

if we have (n-1)n(n+1) well one of them is definetly a multiple of 3....

so (1) says 2 is not a factor of n...

well we know that [(n-1)(n)(n+1)]/24= 1/8 [(n-1)(n+1)] well we know then that (n-1)(n+1) both have at least three factors of 2....so the remainder r =0....

sufficient.

(11)
3 is not a factor of n...well then it means either N-1 or N+1 is a factor of 3...so we have n as a factor of 2...but we dont know anything about n+1 or n vice versa....so insufficient....we cant tell how many factors of 2 are there in n+1....

A it is...
Director
Director
avatar
Joined: 27 Dec 2004
Posts: 910
Followers: 1

Kudos [?]: 10 [0], given: 0

GMAT Tests User
 [#permalink] New post 30 Sep 2005, 11:59
fresinha12 wrote:
Ok lets see....

if we have (n-1)n(n+1) well one of them is definetly a multiple of 3....

so (1) says 2 is not a factor of n...

well we know that [(n-1)(n)(n+1)]/24= 1/8 [(n-1)(n+1)] well we know then that (n-1)(n+1) both have at least three factors of 2....so the remainder r =0....

sufficient.

(11)
3 is not a factor of n...well then it means either N-1 or N+1 is a factor of 3...so we have n as a factor of 2...but we dont know anything about n+1 or n vice versa....so insufficient....we cant tell how many factors of 2 are there in n+1....

A it is...


Freshina12, the stem says (n+1) (n-1). thus C it is
SVP
SVP
User avatar
Joined: 28 May 2005
Posts: 1743
Location: Dhaka
Followers: 6

Kudos [?]: 27 [0], given: 0

GMAT Tests User
 [#permalink] New post 01 Oct 2005, 12:16
Can you guys explain it little more.....
_________________

hey ya......

Senior Manager
Senior Manager
avatar
Joined: 30 Oct 2004
Posts: 289
Followers: 1

Kudos [?]: 4 [0], given: 0

GMAT Tests User
 [#permalink] New post 01 Oct 2005, 12:43
nakib77 wrote:
Can you guys explain it little more.....


I don't know if this is the easiest way to explain .. but from the stem..
For any number n>0 => (n-1)(n+1) has to be a factor of either 2 or 3 or both (plug some random values.. say n =59 => (58)(60) =>2,3,6 factors or say n=26 =>(25)(27) => 3 is a factor)

1) 2 is not a factor of n, out example of 59 shows r will be 0 but [edited: should consider something greater than 24] n=27, (26)(28) r is not zero. Insuff
2) 3 say n=26, (25)(27) divided by 24 will give some remainder r but this value again varies for every even value of n you consider. Insuff.

1&2 ... picking numbers is easy (since it cannot be a multiple of 2,3 or 6) ... say 49.. i.e. (48)(50) => r=0, or n=121 (120)(122) => r=0. So r=0 now for all values on n which is not a multiple of 2,3,6.

May not be the best explanation...But hope that helps.
_________________

-Vikram

Senior Manager
Senior Manager
avatar
Joined: 30 Oct 2004
Posts: 289
Followers: 1

Kudos [?]: 4 [0], given: 0

GMAT Tests User
 [#permalink] New post 01 Oct 2005, 16:06
duttsit wrote:
the only thing i remember is that any number of the form (n^2 - 1) is divisible by 24 if n is prime > 3.


That's a real nice tip. Didn't know that.
_________________

-Vikram

Manager
Manager
User avatar
Joined: 03 Aug 2005
Posts: 134
Followers: 1

Kudos [?]: 2 [0], given: 0

 [#permalink] New post 03 Oct 2005, 04:00
Why is n = 1 excluded?

1 is a positive integer and 2 and 3 are not factors of 1.
Senior Manager
Senior Manager
User avatar
Joined: 14 Apr 2005
Posts: 422
Location: India, Chennai
Followers: 1

Kudos [?]: 3 [0], given: 0

GMAT Tests User
Re: ds#positive integer [#permalink] New post 04 Oct 2005, 02:15
nakib77 wrote:
OA to be followed....


My answer is A. The equn can be simplified as n^2 -1

From 1, 2 is not a factor of n. which mean n has to be odd.
If n = 3 then n ^2 -1 = 8 when divided by 24 gives the remanider 8.
If n = 5 then n ^ 2 - 1 = 24 gives the remainder 0.
If n = 7 then n ^ 2 - 1 = 48 gives the remainder 0.

So n should be 3.

From 2, 3 is not a factor of n. so either n or n+1 should be a factor of 2. This leaves us with more than one answer to choose. So B is not sufficient.

Hence my answer is A.
Re: ds#positive integer   [#permalink] 04 Oct 2005, 02:15
    Similar topics Author Replies Last post
Similar
Topics:
integers ritula 4 29 Jan 2009, 03:22
Integers ventivish 1 16 May 2008, 12:19
integer nick_sun 4 11 Jun 2007, 05:58
Integers nick_sun 2 22 Mar 2007, 00:49
integers vikasgaba 5 10 Jan 2006, 09:25
Display posts from previous: Sort by

ds#positive integer

  Question banks Downloads My Bookmarks Reviews Important topics  


GMAT Club MBA Forum Home| About| Privacy Policy| Terms and Conditions| GMAT Club Rules| Contact| Sitemap

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®.