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What is the difference between the average (arithmetic mean) of the fi

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Math Revolution GMAT Instructor
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New post 19 Apr 2018, 02:49
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Question Stats:

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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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Re: What is the difference between the average (arithmetic mean) of the fi  [#permalink]

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New post 19 Apr 2018, 07:13
I think I have the problem to understand the question

First 9 positive integers are 1,2,3,4,5,6,7,8,9 the average (9+1)/2=5
Second 9 non-negative integers: 9,10,11,12,13,14,15,16,17 the average (9+17)/2=13 I included 9 in this set, because 0 is the first non-negative integer and so the first 9 non-negative integers are 0,1,2,3,4,5,6,7,8
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Re: What is the difference between the average (arithmetic mean) of the fi  [#permalink]

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New post 19 Apr 2018, 07:18
MathRevolution 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

First 9 positive integers : 1, 2, 3, 4, 5, 6, 7, 8, 9 -> Average-> 5
Non-negative integers start from 0. Here we are asked for second non-negative integer. So, second 9 non-negative integers : 1, 2, 3, 4, 5, 6, 7, 8, 9 -> Average-> 5
Hence Difference is 0
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Re: What is the difference between the average (arithmetic mean) of the fi  [#permalink]

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New post 19 Apr 2018, 12:41
This question is worded awkwardly. "The second nine" non negative integers. I know what a non negative integer is, but the phrase "second nine" could be phrased a lot better
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Re: What is the difference between the average (arithmetic mean) of the fi  [#permalink]

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New post 22 Apr 2018, 18:28
=>

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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What is the difference between the average (arithmetic mean) of the fi  [#permalink]

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New post 23 Apr 2018, 05:10
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MathRevolution wrote:
=>

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.


MathRevolution please elaborate ...how come the second 9 non-negative integers are 1, 2, 3, …, 9

My understanding the second 9 non-negative integers would start after the first 9 non-negative integers ( 0, 1, 2, …, 8) which would make it (9, 10, ....17)

Thanks in advance
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