It is currently 21 Oct 2017, 11:04

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

DS-Divisible by 4.jpg

  post reply Question banks Downloads My Bookmarks Reviews Important topics  
Author Message
Manager
Manager
User avatar
Joined: 21 May 2008
Posts: 85

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

DS-Divisible by 4.jpg [#permalink]

Show Tags

New post 10 Oct 2008, 06:46
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.

Attachment:
DS-Divisible by 4.jpg
DS-Divisible by 4.jpg [ 8.66 KiB | Viewed 967 times ]

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

Director
Director
User avatar
Joined: 27 Jun 2008
Posts: 540

Kudos [?]: 69 [0], given: 92

WE 1: Investment Banking - 6yrs
Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 07:35
(1) k = 2
n = 5

n^3-n = 125 - 5 = 120.....Yes

k=1
n=3

n^3 - n = 27-3 = 24...Yes

Suff

(2) n^2+n = n(n+1) / 6

Let n = 2

n^3 - n = 2^3-2 = 6...not divisible by 4

n = 5

n^3 - n = 120..divisible by 4

Insuff

A

Kudos [?]: 69 [0], given: 92

Senior Manager
Senior Manager
User avatar
Joined: 04 Aug 2008
Posts: 372

Kudos [?]: 37 [0], given: 1

Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 07:36
klb15 wrote:
Attachment:
DS-Divisible by 4.jpg


no easy way here

started from plugin in 1 and that eliminated 1)
then proceeded with 2 and with all the combinations it turned out that only numbers divisible w 6 but greater then 6 will satisfy, therefore C
_________________

The one who flies is worthy. The one who is worthy flies. The one who doesn't fly isn't worthy

Kudos [?]: 37 [0], given: 1

Senior Manager
Senior Manager
User avatar
Joined: 04 Aug 2008
Posts: 372

Kudos [?]: 37 [0], given: 1

Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 07:43
pawan203 wrote:
(1) k = 2
n = 5

n^3-n = 125 - 5 = 120.....Yes

k=1
n=3

n^3 - n = 27-3 = 24...Yes

Suff

(2) n^2+n = n(n+1) / 6

Let n = 2

n^3 - n = 2^3-2 = 6...not divisible by 4

n = 5

n^3 - n = 120..divisible by 4

Insuff

A


if n is 2 then satisfies 1) but not the question 8-2=6 not divisible
_________________

The one who flies is worthy. The one who is worthy flies. The one who doesn't fly isn't worthy

Kudos [?]: 37 [0], given: 1

VP
VP
User avatar
Joined: 30 Jun 2008
Posts: 1034

Kudos [?]: 708 [0], given: 1

Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 07:50
I guess there is an easy way here.

\(n^3 -n\) = \(n(n^2-1)\) = n(n+1)(n-1)

The question is is (n-1)*n*(n+1) divisible by 4 ? ( notice n-1, n and n+1 are consecutive numbers)

(1) n=2k+1 . This essentially means n is odd. so n-1 and n+1 are evens.

Rule: When an integer can be divided by 2 twice, it is divisible by 4 as well.

Now as we have 2 evens, it is divisible by 2 twice or in other words it is divisible by 4.
So statement 1 is sufficient

(2) \(n^2+n\) is divisible by 6 or n(n+1) is divisible by 6.
So either n or n+1 is a multiple of 2 and the other is multiple of 3. To determine whether a number is divisible by 4, we have to check if it is divisible by 2 twice. Now in statement 2 we do not know if n is even or odd. So cant say

Is the answer A ?
_________________

"You have to find it. No one else can find it for you." - Bjorn Borg

Kudos [?]: 708 [0], given: 1

Manager
Manager
avatar
Joined: 15 Apr 2008
Posts: 164

Kudos [?]: 12 [0], given: 1

Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 13:17
i am also getting answer A

i did it by picking odd and even numbers.

Kudos [?]: 12 [0], given: 1

SVP
SVP
User avatar
B
Joined: 05 Jul 2006
Posts: 1750

Kudos [?]: 431 [0], given: 49

GMAT ToolKit User
Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 10 Oct 2008, 16:05
N(N+1)(N-1) ARE 3 CONSECS

IF N IS ODD THEN SURE IS DEVISBALE BY 4 IF N IS EVEN THEN IT COULD BE EITHER DEVISABLE BY 2 OR 4

FROM ONE

n IS ODD.......SUFF

FROM 2

N(N+1) IS DEVISBALE BY 6

WE STILL DONT KNOW IF N IS EVEN OR ODD.....INSUFF

a

Kudos [?]: 431 [0], given: 49

Manager
Manager
avatar
Joined: 10 Aug 2008
Posts: 74

Kudos [?]: 13 [0], given: 0

Re: DS-Divisible by 4 [#permalink]

Show Tags

New post 11 Oct 2008, 11:29
Quest is n3-n is divisible by 4
OR
n(n-1)(n+1) is divisible by 4.

Now state 1
------------

n = 2k + 1 => (n-1) = 2k means n-1 always divisible by 2

2nd state
---------
n^2 + n is divisible by 6.
=> n(n+1) is divisible by 6

so n(n-1)(n+1) is divisible by 12 Hence divisible bhy 4

Ans is C)

Kudos [?]: 13 [0], given: 0

Re: DS-Divisible by 4   [#permalink] 11 Oct 2008, 11:29
Display posts from previous: Sort by

DS-Divisible by 4.jpg

  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®.