Bunuel wrote:
If the average (arithmetic mean) of p and r is n and the average (arithmetic mean) of r and s is 3n, what is the value of s – p?
A. 4n
B. 2n
C. n
D. n + r
E. n + 2r
We can create the equations:
(p + r)/2 = n
p + r = 2n
p = 2n - r
and
(r + s)/2 = 3n
r + s = 6n
s = 6n - r
Thus, s - p = (6n - r) - (2n - r) = 4n.
Answer: A