Clarification

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knight247: Legendary Member; Posts: 504; Joined: Tue Apr 19, 2011 1:40 pmFollowed by: 11 members; Thanked: 114 times

by knight247 » Sat Jul 23, 2011 12:10 am

If k and n are integers, is n divisible by 7?
(1) n/2-3=k
(2) 2k-1 is divisible by 7

The OA is C. But I disagree with it. It should be A according to me

Here's why
(1) n/2-3=k

Rewritten as (n-6)/2=k
n-6=2k
n=2k+6

Now 2k and 6 are both even numbers. Even+Even=Even. Hence, n is even. If n is even then it can't be divisible by 7. Am I making sense?

(2)
2k-1 is divisible by 7
Gives no hints on the divisibility of n hence insufficient.

Answer is A

Thoughts, Comments? lol

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Source: Beat The GMAT — Data Sufficiency | Sat Jul 23, 2011 12:10 am

cans: Legendary Member; Posts: 1309; Joined: Mon Apr 04, 2011 5:34 amFollowed by: 123 members; Location: India; Thanked: 310 times; GMAT Score:750

by cans » Sat Jul 23, 2011 12:27 am

(1) n/2-3=k

Rewritten as (n-6)/2=k
n-6=2k
n=2k+6

Now 2k and 6 are both even numbers. Even+Even=Even. Hence, n is even. If n is even then it can't be divisible by 7.

14 is even and also divisible by 7.
So answer is C

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Cans!!

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knight247: Legendary Member; Posts: 504; Joined: Tue Apr 19, 2011 1:40 pmFollowed by: 11 members; Thanked: 114 times

by knight247 » Sat Jul 23, 2011 12:45 am

Whooops...My Bad..lol

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Ozlemg: Master | Next Rank: 500 Posts; Posts: 407; Joined: Tue Jan 25, 2011 9:19 amFollowed by: 7 members; Thanked: 25 times

by Ozlemg » Mon Jul 25, 2011 2:18 am

knight247 wrote:If k and n are integers, is n divisible by 7?
(1) n/2-3=k
(2) 2k-1 is divisible by 7

The OA is C. But I disagree with it. It should be A according to me

Here's why
(1) n/2-3=k

Rewritten as (n-6)/2=k
n-6=2k
n=2k+6

Now 2k and 6 are both even numbers. Even+Even=Even. Hence, n is even. If n is even then it can't be divisible by 7. Am I making sense?

(2)
2k-1 is divisible by 7
Gives no hints on the divisibility of n hence insufficient.

Answer is A

Thoughts, Comments? lol

Here is my way :

plug K to statement 2 and the number will still be divisible by 7.

so, 2*(n/2-3)-1 = n-7 is divisible by 7. (for ex : 14-7, 28-7 etc.)

Hence, C

The more you suffer before the test, the less you will do so in the test!

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