kaplan #18

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kaplan #18

by magical cook » Wed Aug 22, 2007 5:17 pm
23) Are the integers q, r, and s consecutive?
1) The average (arithmetic mean) of q, r, and s is r.
2) r-q = s-r


Hi Can anyone help pls? Correct answer will follow. thanks!

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by agps » Thu Aug 23, 2007 3:26 am
1- try out with real numbers

2+3+4=9 9/3=3, true
4+5+6= 15 15/3=5, true
7+8+9=24 24/3=8, true
1 is sufficient

2- r-q=s-r

not sufficient
q=2
r=4
s=6
4-2=2
6-4=2

answer is A

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by krishnamurthyu » Thu Aug 23, 2007 5:18 am
Given: q,r,s :
is q,r,s consecative

1) The average (arithmetic mean) of q, r, and s is r.

let q,r,s :x,x+a,x+2a

Avg= ( x+ x+a+ x+2a )/3= (x+a)
3x + 3a = 3 (x+a) : True .

iAns: AD

2) r-q = s-r
r-q : x+a - x = a
s-r : x+2a - (x + a) = a :

True:

Ans:D.

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by beny » Thu Aug 23, 2007 6:14 am
(10+15+20)/3 = 15
20-15 = 15-10

Answer: E

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by agps » Thu Aug 23, 2007 6:32 am
nice point beny ;)

agreed

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by beny » Thu Aug 23, 2007 10:36 am
Anonymous wrote:This is a common GMAT trap.
The difference between consecutive and "evenly spaced"
In evenly spaced, the avg. is the highest,+ lowest term / 2. But they are not neccesarily consecutive, as they can be 2,4,6,8 for example.
In this case they are evenly spaced, not consecutive.
Three consecutive integers are also evenly spaced. Therefore, you can't definitively say that they aren't consecutive.

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by magical cook » Thu Aug 23, 2007 10:46 am
Thanks for responses. :D

Beny got it right - OA is E)