If a = (1/2)b and c = 5a, then which of the following represents the average (arithmetic mean) of a, b, and c, in terms of a ?  Select the correct option:
A) (8/3)a
B) (11/3)a
C) 4a
D) (4 1/7)a
E) (7 1/4)a
Official Answer: A   The average of the three variables isa + b + c/3. However, we need to solve in terms of a, which means we must convert b and c into something in terms of a.   Were told that a =1/2b, which is equivalent to b = 2a. We can plug that in and simplify the average to:a + 2a + c/3   We also know that c = 5a, which we can plug directly into the average expression:   a + 2a + 5a/3   = 8a/3 = (8/3)a, choice(8/3)a.
<result>A</result>
If a = (1/2)b and c = 5a, then which of the following represents the average (arithmetic mean) of a, b, and c, in terms of a ?