The number line shown contains three points R, S, and T

[Gmat_mission]

The number line shown contains three points R, S, and T, whose coordinates have absolute values r, s, and t, respectively. Which of the following equals the average (arithmetic mean) of the coordinates of the points R, S, and T?

A. s
B. s + t - r
C. (r - s - t)/3
D. (r + s + t)/3
E. (s + t - r)/3

[spoiler]OA=E[/spoiler]

Source: Official Guide

[GMATGuruNY]

The number line shown contains three points R, S, and T, whose coordinates have absolute values r, s, and t, respectively. Which of the following equals the average (arithmetic mean) of the coordinates of the points R, S, and T?

A. s
B. s + t - r
C. (r - s - t)/3
D. (r + s + t)/3
E. (s + t - r)/3

Let R=-3, S=3 and T=6, implying that r=|-3|=3, s=|3|=3, and t=|6|=6.
Average of R, S, and T = (-3+3+6)/3 = 2.
The correct answer must yield 2 when r=3, s=3 and t=6.
Only E works:
(s + t - r)/3 = (3+6-3)/3 = 6/3 = 2

The correct answer is E.

[Scott@TargetTestPrep]

The number line shown contains three points R, S, and T, whose coordinates have absolute values r, s, and t, respectively. Which of the following equals the average (arithmetic mean) of the coordinates of the points R, S, and T?

A. s
B. s + t - r
C. (r - s - t)/3
D. (r + s + t)/3
E. (s + t - r)/3

[spoiler]OA=E[/spoiler]

Source: Official Guide

We can let R, S, and T be the actual values. Thus, we want to determine the value of (R + S + T)/3. Since S and T are positive, S = s and T = t. However, since R is negative, R = -r. Thus, the average becomes:

(-r + s + t)/3

(s + t - r)/3

Answer: E