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# The mean of four integers will not change if all the

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SVP
Joined: 04 May 2006
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The mean of four integers will not change if all the [#permalink]  14 May 2008, 02:13
The mean of four integers will not change if all the integers are multiplied by any constant. What is always true about this set of numbers?

I. The mean of the set is 0

II. The sum of the largest member and the smallest member of the set is 0

III. The set contains both positive and negative integers

I only
II only
III only
I and II only
I, II, and III
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CEO
Joined: 17 Nov 2007
Posts: 3574
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
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Kudos [?]: 2247 [0], given: 359

Re: M12-30 [#permalink]  14 May 2008, 03:15
Expert's post
I guess I and III, but this onption is not included here.

I. if we write out the formula of mean, we can easily find that mean has to be 0

II. {-3,-1, 0,4} satisfies the condition, but the sum of the largest member and the smallest member of the set is 4-3=1

III. A set of something means in GMAT non repetitive list. So, the set has to contain positive and negative integers to have the mean=0. {0,0,0,0} - is not a set in GMAT.
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Joined: 28 Dec 2004
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Location: New York City
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Re: M12-30 [#permalink]  14 May 2008, 04:09
i think its 1 only..

we could have all 0s in the set as well..

{0,0,0} where the mean=0

sum of largest+smallest=0..

and it doesnt have to have negative or positive integers..
CEO
Joined: 17 Nov 2007
Posts: 3574
Concentration: Entrepreneurship, Other
Schools: Chicago (Booth) - Class of 2011
GMAT 1: 750 Q50 V40
Followers: 414

Kudos [?]: 2247 [0], given: 359

Re: M12-30 [#permalink]  14 May 2008, 05:26
Expert's post
the question about set is still open for me (look at 7-t61572)

I have not seen so far at least one real GMAT problem that tests the set concept. So, I think that problems like this one do not reflect real GMAT.
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Current Student
Joined: 28 Dec 2004
Posts: 3387
Location: New York City
Schools: Wharton'11 HBS'12
Followers: 14

Kudos [?]: 186 [0], given: 2

Re: M12-30 [#permalink]  14 May 2008, 06:06
walker wrote:
the question about set is still open for me (look at 7-t61572)

I have not seen so far at least one real GMAT problem that tests the set concept. So, I think that problems like this one do not reflect real GMAT.

i remember having this issue at college in Computer sci..sets contain unique different integers..however mathematically a set can have repeating numbers..i believe OG prefers the mathematical definition
SVP
Joined: 04 May 2006
Posts: 1936
Schools: CBS, Kellogg
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Kudos [?]: 491 [0], given: 1

Re: M12-30 [#permalink]  15 May 2008, 20:10
Thanks Walker and fresinha12. Your reasoning really helps me out on this, and ofcourse be better than OE.

OA is A
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Re: M12-30   [#permalink] 15 May 2008, 20:10
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