• 7 CATs FREE!
    If you earn 100 Forum Points

    Engage in the Beat The GMAT forums to earn
    100 points for $49 worth of Veritas practice GMATs FREE

    Veritas Prep
    VERITAS PRACTICE GMAT EXAMS
    Earn 10 Points Per Post
    Earn 10 Points Per Thanks
    Earn 10 Points Per Upvote
    REDEEM NOW
This topic has expert replies
Senior | Next Rank: 100 Posts
Posts: 38
Joined: 08 Nov 2008

GMAT Prep.

by sumittaneja009 » Mon Jan 19, 2009 12:07 am
If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?
1). n is not divisible by 2
2). n is not divisible by 3


Please explain?

User avatar
Legendary Member
Posts: 2134
Joined: 20 Oct 2008
Thanked: 237 times
Followed by:25 members
GMAT Score:730

Re: GMAT Prep.

by logitech » Mon Jan 19, 2009 12:14 am
If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?

1). n is not divisible by 2

So n is an odd number

n=1 - 0
n=3 - 8
n=5 - 0

INSUF ( I did not catch the n=3 case before )

2). n is not divisible by 3

n=1 - 0

n=2 - 3

Insuf

Together we know that n can not be 3 and n will be an ODD number

1, 5, 7, 11 and for all of these number the remainder will be 0

Choose C :oops:
Last edited by logitech on Mon Jan 19, 2009 9:52 am, edited 1 time in total.
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"

Senior | Next Rank: 100 Posts
Posts: 79
Joined: 06 Feb 2008
Thanked: 2 times
GMAT Score:620

by yalanand » Mon Jan 19, 2009 9:31 am
Logitech could you please explain me about this ??

1). n is not divisible by 2

So n is an odd number

n=1 - 0
n=3 - 0
n=5 - 0

So We will always get 0 as a remainder SUF

How is this sufficient ??

User avatar
Legendary Member
Posts: 2134
Joined: 20 Oct 2008
Thanked: 237 times
Followed by:25 members
GMAT Score:730

by logitech » Mon Jan 19, 2009 9:49 am
yalanand wrote:Logitech could you please explain me about this ??

1). n is not divisible by 2

So n is an odd number

n=1 - 0
n=3 - 0
n=5 - 0

So We will always get 0 as a remainder SUF

How is this sufficient ??
If n is a positive integer and r is the remainder when (n-1)(n+1) is divided by 24, what is the value of r?

So we are asked to find the remainder. And in the first statement we all have 0 as the remainder when the number is divided by 24.

For example n=5

(n-1)(n+1) = 4x6=24 divided by 24 , remainder is 0

Now looking at my previous post, I realized that the only ODD number that will leave a different remainder is n=3

2x4=8 and when is divided by 24 , the remainder is 8 :shock:

So it seems like A can not be sufficient because of the n=3 case.

Let's say what other will have to say :roll:
LGTCH
---------------------
"DON'T LET ANYONE STEAL YOUR DREAM!"