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of x and y?

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by sanju09 » Thu Sep 16, 2010 10:13 pm
What is the average (arithmetic mean) of x and y?

(1) The average (arithmetic mean) of (x + 1) and (y - 1) is equal to the average (arithmetic mean) of x and y.

(2) The average (arithmetic mean) of x, y, and -1 is 1.

ORIGINAL SOURCE OF THIS QUESTION:
https://www.west.net/~stewart/gmat/
The mind is everything. What you think you become. -Lord Buddha



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Source: — Data Sufficiency |
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by sumit.sinha » Sat Sep 18, 2010 5:44 am
sanju09 wrote:What is the average (arithmetic mean) of x and y?

(1) The average (arithmetic mean) of (x + 1) and (y - 1) is equal to the average (arithmetic mean) of x and y.

(2) The average (arithmetic mean) of x, y, and -1 is 1.


[spoiler]Source: https://www.west.net/~stewart/gmat[/spoiler]
what is (x+y) ?

(1) (x+1 + y -1)/2 = (x+y)/2
i.e. (x+y)/2 = (x+y)/2
(x+y) could be 0,1,2...and so on anything. INSUFFICIENT

(2) (x+y-1)/3 =1
i.e. x+ y = 4
SUFFICIENT

CORRECT ANSWER (B) IMO.
Cheers,
Sumit
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by puneetdua » Sat Sep 18, 2010 8:43 am
One more vote for B.
Thanks
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by tpr-becky » Sun Sep 19, 2010 8:12 pm
I agree - the first statement only tells you what you already know becuase the +1 and -1 cancel each other out.

The second statement gives you another equation from which you can determine the value of x+y which is all you really need tofind their average.
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