It is currently 22 Sep 2017, 08:30

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.

Close

Request Expert Reply

Confirm Cancel

Events & Promotions

Events & Promotions in June
Open Detailed Calendar

If n is +ve integer, is n*n*n - n divided by 4? 1) n=2k+1 ,

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Senior Manager
Senior Manager
User avatar
Joined: 04 Sep 2008
Posts: 251

Kudos [?]: 98 [0], given: 9

Location: Kolkata
Schools: La Martiniere for Boys
If n is +ve integer, is n*n*n - n divided by 4? 1) n=2k+1 , [#permalink]

Show Tags

New post 27 Oct 2008, 05:12
00:00
A
B
C
D
E

Difficulty:

(N/A)

Question Stats:

0% (00:00) correct 0% (00:00) wrong based on 0 sessions

HideShow timer Statistics

This topic is locked. If you want to discuss this question please re-post it in the respective forum.

If n is +ve integer, is n*n*n - n divided by 4?
1) n=2k+1 , where k is an integer
2) n*n + n is divided by 6


Please explain your answers
_________________

Thanks
rampuria

Kudos [?]: 98 [0], given: 9

Intern
Intern
avatar
Joined: 09 May 2008
Posts: 12

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

Location: Trieste, Italy
Re: Number property DS [#permalink]

Show Tags

New post 27 Oct 2008, 06:30
I would say A.

Consider this: n*n*n - n => n(n*n-1) => n(n-1)(n+1).
Look at this as the product of 3 consecutive integers: (n-1)n(n+1).
We're being asked if this product is divisible by 4, and it'll be if at least 2 terms are even (because this means that there are two 2's as a factor of this product).

1) n=2k+1
this tells us that n is odd (if k is even, say k=2, then n=5; if k is odd, say k=3, then n=7). Thus, (n-1) and (n+1) are even; if two terms are even, then n*n*n - n is divisible by 4 => SUFFICIENT

2) n*n + n is divisible by 6
this only means that the product n(n+1) has 2 & 3 as factors. However, we don't know which term is even and which one is odd, consequentely we don't what (n-1) is => INSUFFICIENT

Rampuria, where did you sourced did from?
OA?

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

SVP
SVP
User avatar
B
Joined: 05 Jul 2006
Posts: 1742

Kudos [?]: 418 [0], given: 49

GMAT ToolKit User
Re: Number property DS [#permalink]

Show Tags

New post 27 Oct 2008, 09:14
If n is +ve integer, is n*n*n - n divided by 4?
1) n=2k+1 , where k is an integer
2) n*n + n is divided by 6


Please explain your answers[/quote]

IS N(N^2 - 1) DEVISABLE BY 4

N(N+1)(N-1) 3 CONSECS.DEVISABLE BY 4 IF ( N-1) OR N+1 IS EVEN OR N IS DEVIABLE BY 4

FROM 1

N IS ODD...........SUFF

FROM 2


N(N+1) IS DEVIABLE BY 6

ONE OF THEM IS DEVIABLE BY 2 AS THE OTHER IS ODD........INSUFF

A

Kudos [?]: 418 [0], given: 49

Re: Number property DS   [#permalink] 27 Oct 2008, 09:14
Display posts from previous: Sort by

If n is +ve integer, is n*n*n - n divided by 4? 1) n=2k+1 ,

  post reply Question banks Downloads My Bookmarks Reviews Important topics  


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

Powered by phpBB © phpBB Group | Emoji artwork provided by EmojiOne

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®.