kaplan #18

[magical cook]

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!

[agps]

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

[krishnamurthyu]

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+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.

[beny]

(10+15+20)/3 = 15
20-15 = 15-10

Answer: E

[agps]

nice point beny

agreed

[beny]

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.

[magical cook]

Thanks for responses.

Beny got it right - OA is E)