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# Is x divisible by 30? (1) X = k*(m^3 - m), where m and k are

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SVP
Joined: 05 Jul 2006
Posts: 1516
Followers: 5

Kudos [?]: 127 [1] , given: 39

Is x divisible by 30? (1) X = k*(m^3 - m), where m and k are [#permalink]  10 Aug 2009, 09:57
1
KUDOS
00:00

Difficulty:

(N/A)

Question Stats:

50% (11:23) correct 50% (02:20) wrong based on 2 sessions
Is x divisible by 30?

(1) X = k*(m^3 - m), where m and k are both integers > 9
(2) X = n^5 - n, where n is an integer > 9
Manager
Joined: 10 Jul 2009
Posts: 169
Followers: 1

Kudos [?]: 44 [0], given: 8

Re: divisibility - good one [#permalink]  10 Aug 2009, 10:06
1) X = k*(m^3 -m)
= K*m*(m-1)*(m+1)
Give K and m are > 9
X is definitely divisible by 2,3 but not by 5.
2)X = n^5 - n
= n*(n^4 - 1)
= n*(n^2 + 1)(n-1)(n + 1)
given n > 9
So for any value of n the value is divisible by 2,3,5.
Manager
Status: Applying
Joined: 18 Jul 2009
Posts: 155
Location: United Kingdom
Concentration: General Management, Strategy
GPA: 3.65
WE: Consulting (Telecommunications)
Followers: 1

Kudos [?]: 11 [0], given: 6

Re: divisibility - good one [#permalink]  10 Aug 2009, 21:53
thanks for the above answer but plz cud you explain how

n(n^2 + 1)(n+1)(n-1) is divisible by 5 ? Or is it a standard thing that i am missing ....

SVP
Joined: 05 Jul 2006
Posts: 1516
Followers: 5

Kudos [?]: 127 [1] , given: 39

Re: divisibility - good one [#permalink]  10 Aug 2009, 23:28
1
KUDOS
AshForGMAT wrote:
thanks for the above answer but plz cud you explain how

n(n^2 + 1)(n+1)(n-1) is divisible by 5 ? Or is it a standard thing that i am missing ....

TRY PLUGING IN NUMBER ( N>9)... U WILL SEE FOR UR SELF
Director
Joined: 01 Apr 2008
Posts: 904
Schools: IIM Lucknow (IPMX) - Class of 2014
Followers: 18

Kudos [?]: 332 [0], given: 18

Re: divisibility - good one [#permalink]  15 Aug 2009, 12:17
Good one yezz +1. Keep them coming:)
Re: divisibility - good one   [#permalink] 15 Aug 2009, 12:17
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