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If n is a positive integer and r is the remainder when 4+7n

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If n is a positive integer and r is the remainder when 4+7n [#permalink]

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New post 13 Oct 2008, 19:57
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If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20

Kudos [?]: 24 [0], given: 0

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Kudos [?]: 832 [0], given: 19

Re: DS Problem [#permalink]

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New post 13 Oct 2008, 21:09
udribat wrote:
If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20


A.

1: n+1 = 3k, where k is an integer. so if n is divided by 3, the reminder is 2. then when 7n is divided by 3, reminder is 2. so 2+4 is 6. then r = 0.

2: n > 20 tells nothing. nsf.
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Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
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Re: DS Problem [#permalink]

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New post 13 Oct 2008, 21:19
GMAT TIGER wrote:
udribat wrote:
If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20


A.

1: n+1 = 3k, where k is an integer. so if n is divided by 3, the reminder is 2. then when 7n is divided by 3, reminder is 2. so 2+4 is 6. then r 0.
2: n > 20 tells nothing. nsf.

everything is correct, just wanted to add that (4+7n)/3=4/3+7n/3=4/3+2

Kudos [?]: 61 [0], given: 2

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Re: DS Problem [#permalink]

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New post 13 Oct 2008, 22:03
udribat wrote:
If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20


alternatively:

1: n + 1 = 3k where k is an integer.
4 + 7n = 1+1+1+1+n+n+n+n+3n = 4(1+n) + 3n

in the above expression, 4(1+n) is divisible by 3, r is 0 for this one. 3n is less than 3(n+1) or (3n + 3) by 3. if n+1 is divisible by 3, then (3n+3) is also divisibly by 3. also divisibly by 3 is any addition or substraction of any value that is multiple of 3.

so (3n + 3) - 3 = 3n, whcih is also divisibly by 3. so r = 0.

2: n > 20 doesnot tell much about its divisibility by 3.
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Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


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Re: DS Problem [#permalink]

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New post 13 Oct 2008, 22:06
kazakhb wrote:
GMAT TIGER wrote:
udribat wrote:
If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20


A.

1: n+1 = 3k, where k is an integer. so if n is divided by 3, the reminder is 2. then when 7n is divided by 3, reminder is 2. so 2+4 is 6. then r 0.
2: n > 20 tells nothing. nsf.

everything is correct, just wanted to add that (4+7n)/3 = 4/3 + 7n/3 = 4/3 + 2


check again the highlighted part, whcih is not correct and should be (4/3 + 2/3), above.
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Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


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Kudos [?]: 832 [0], given: 19

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Re: DS Problem [#permalink]

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New post 13 Oct 2008, 22:45
udribat wrote:
If n is a positive integer and r is the remainder when 4+7n is divided by 3, what is the value of r?

1) n+1 is divisible by 3

2) n > 20



From stmt1: n + 1 = 3x for x = 0, 1,2,3,....
OR, n = 3x - 1

Thus, 7n + 4 = (21x - 3) and this is divisible by 3 for any value of x. Hence, sufficient.

Stmt2 is not sufficient.

Kudos [?]: 278 [0], given: 0

Manager
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Re: DS Problem [#permalink]

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New post 14 Oct 2008, 01:45
Quote:

check again the highlighted part, whcih is not correct and should be (4/3 + 2/3), above.

ohhh, right, man; my mistake

Kudos [?]: 61 [0], given: 2

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Re: DS Problem [#permalink]

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New post 14 Oct 2008, 07:21
kazakhb wrote:
Quote:

check again the highlighted part, whcih is not correct and should be (4/3 + 2/3), above.

ohhh, right, man; my mistake


check again the highlighted part, (which is not correct). :lol: :lol:
_________________

Verbal: http://gmatclub.com/forum/new-to-the-verbal-forum-please-read-this-first-77546.html
Math: http://gmatclub.com/forum/new-to-the-math-forum-please-read-this-first-77764.html
Gmat: http://gmatclub.com/forum/everything-you-need-to-prepare-for-the-gmat-revised-77983.html


GT

Kudos [?]: 832 [0], given: 19

Manager
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User avatar
Joined: 01 Jan 2008
Posts: 222

Kudos [?]: 61 [0], given: 2

Schools: Booth, Stern, Haas
Re: DS Problem [#permalink]

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New post 14 Oct 2008, 21:08
GMAT TIGER wrote:
kazakhb wrote:
Quote:

check again the highlighted part, whcih is not correct and should be (4/3 + 2/3), above.

ohhh, right, man; my mistake


check again the highlighted part, (which is not correct). :lol: :lol:

really?

Kudos [?]: 61 [0], given: 2

Re: DS Problem   [#permalink] 14 Oct 2008, 21:08
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If n is a positive integer and r is the remainder when 4+7n

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