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What is the difference between the av

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by Max@Math Revolution » Thu Apr 19, 2018 1:41 am

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[GMAT math practice question]

What is the difference between the average (arithmetic mean) of the first 9 positive integers and the average (arithmetic mean) of the second 9 non-negative integers?

A. 0
B. 1
C. 2
D. 3
E. 4
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by regor60 » Thu Apr 19, 2018 5:03 am
Max@Math Revolution wrote:[GMAT math practice question]

What is the difference between the average (arithmetic mean) of the first 9 positive integers and the average (arithmetic mean) of the second 9 non-negative integers?

A. 0
B. 1
C. 2
D. 3
E. 4
The correct answer is not among the choices
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by Max@Math Revolution » Sun Apr 22, 2018 5:21 pm
=>

The first 9 positive integers are 1, 2, 3, ..., 9. Their average is 5.
The second 9 non-negative integers are 1, 2, 3, ..., 9, since the first 9 non-negative integers are 0, 1, 2, ..., 8. Their average is 5 too.

Thus the difference between those averages is 0.

Therefore, A is the answer.
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by regor60 » Mon Apr 23, 2018 6:02 am
This question appears ambiguously worded to me.

I think it would be reasonable to believe the wording "second nine" is intended to exclude any member of the "first nine" and I would hope a GMAT question would clarify.
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by Scott@TargetTestPrep » Tue Apr 24, 2018 10:42 am
Max@Math Revolution wrote:[GMAT math practice question]

What is the difference between the average (arithmetic mean) of the first 9 positive integers and the average (arithmetic mean) of the second 9 non-negative integers?

A. 0
B. 1
C. 2
D. 3
E. 4
The first 9 positive integers are 1, 2, 3, ..., 9.

The first 9 non-negative integers are 0, 1, 2, ..., 8. Thus the second 9 non-negative integers are 1, 2, 3, ..., 9. We see that the problem is talking about two sets of the same integers; thus, the difference between the means is 0.

Answer: A

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