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What is the average (arithmetic mean) of a certain series of

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What is the average (arithmetic mean) of a certain series of [#permalink] New post 20 Apr 2010, 07:22
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What is the average (arithmetic mean) of a certain series of N consecutive integers?

(1) The sum of the terms of the series is N.

(2) The sum of the greatest and least terms is 2.

[Reveal] Spoiler:
D


How should I solve this question? Thanks for your help!
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Re: Average/ Mean [#permalink] New post 20 Apr 2010, 07:46
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sudai wrote:
What is the average (arithmetic mean) of a certain series of N consecutive integers?

(1) The sum of the terms of the series is N.

(2) The sum of the greatest and least terms is 2.

[Reveal] Spoiler:
D


How should I solve this question? Thanks for your help!


Arith. Mean of any series of consecutive integers = (a+l)/2 where a= first integer, l= last integer.
=> Sum of that series = (number of terms in the series)*(Average of the series) = N*(a+l)/2

Stmt 1) given, Sum= N => N*(a+l)/2= N => Mean = 1 => Sufficient info
Stmt 2) given, a+l= 2 => (a+l)/2 or the Mean = 1 => Sufficient info

Answer = D
Intern
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Re: Average/ Mean [#permalink] New post 20 Apr 2010, 07:59
PhunsukWangdu wrote:
sudai wrote:
What is the average (arithmetic mean) of a certain series of N consecutive integers?

(1) The sum of the terms of the series is N.

(2) The sum of the greatest and least terms is 2.

[Reveal] Spoiler:
D


How should I solve this question? Thanks for your help!


Arith. Mean of any series of consecutive integers = (a+l)/2 where a= first integer, l= last integer.
=> Sum of that series = (number of terms in the series)*(Average of the series) = N*(a+l)/2

Stmt 1) given, Sum= N => N*(a+l)/2= N => Mean = 1 => Sufficient info
Stmt 2) given, a+l= 2 => (a+l)/2 or the Mean = 1 => Sufficient info

Answer = D




well explained! Thank you!
Re: Average/ Mean   [#permalink] 20 Apr 2010, 07:59
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