What is the average (arithmetic mean) of eleven consecutive : GMAT Data Sufficiency (DS)
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# What is the average (arithmetic mean) of eleven consecutive

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What is the average (arithmetic mean) of eleven consecutive [#permalink]

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23 Dec 2007, 23:16
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What is the average (arithmetic mean) of eleven consecutive integers?

(1) The average of the first nine integers is 7

(2) The average of the last nine integers is 9
[Reveal] Spoiler: OA

Last edited by stonecold on 21 Dec 2016, 16:47, edited 1 time in total.
Edited the question and added the OA
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Re: What is the average (arithmetic mean) of eleven consecutive [#permalink]

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04 Apr 2011, 21:22
LM wrote:
Hang Tuah wrote:
What is the average (arithmetic mean) of eleven consecutive integers?

(1) The average of the first nine integers is 7

(2) The average of the last nine integers is 9

Scroll down for OA.

From ( i ) you can find the 9th integer

Sum = average*9

sum= n*(n+1)/2

then you can solve.

Second does not help

Should be "A".

OA is D.

Should be D.

For (B):
The average of last 9 numbers: (n+2+n+10)/2=9 --> n=3 --> the range is 3, 4 ...13.
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Re: What is the average (arithmetic mean) of eleven consecutive [#permalink]

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04 Apr 2011, 22:37
S1-9 = 9 * 7 = 63 = n + n + 1 + n + 2.. n + 8

=> 9n + (1+8)/2 * 8 = 63

=>9n + 36 = 63

=> 9n = 27 => n = 3, and the rest can be calculated.

S2-11 = 9 * 9 = 81 => n+2 + ..... + n+10

9n + (2+10)/2 * 9 = 81

=>9n + 54 = 81

=> 9n = 27 => n = 3, and the rest can be calculated.

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Re: What is the average (arithmetic mean) of eleven consecutive [#permalink]

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05 Apr 2011, 06:47

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Re: What is the average (arithmetic mean) of eleven consecutive   [#permalink] 05 Apr 2011, 06:47
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