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# number properties

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Manager
Joined: 04 Sep 2006
Posts: 113

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29 Jan 2009, 10:18
This topic is locked. If you want to discuss this question please re-post it in the respective forum.

q: if n is a +ve integer , what is the remainder when n+1 * n-1 is divided by 24?

1. n is not divisible by 3
2. n is not divisible by 2

pls explain
SVP
Joined: 17 Jun 2008
Posts: 1507

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30 Jan 2009, 01:48
From stmt1:
n = 1,2,4,5,7,8,10, 11, 13, .....
(n-1)(n+1) = 0, 3, 15, 24,....

Hence, when (n-1)(n+1) is divided by 24, the remainder will be different....not sufficient.

From stmt2:
n = 1,3,5,6,7,9,11, .....
(n-1)(n+1) = 0, 8, 24, 48, 80, 120,.....

Hence, when (n-1)(n+1) is divided by 24, the remainder will be different....not sufficient.

Combining stmt1 and stmt2:
(n-1)(n+1) = 0, 24, 48, 120, ......

Hence, when (n-1)(n+1) is divided by 24, the remainder will always be 0.....sufficient.

Hence, C.
Re: number properties   [#permalink] 30 Jan 2009, 01:48
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# number properties

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