If a = (1/6)b and c = 7a, then which of the following represents the average (arithmetic mean) of a, b, and c, in terms of a ?  Pick one
A) a + 4	B) (11/3)a	C) (13/3)a	D) (4 1/7)a	E) (7 1/4)a
Official Answer: C   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 =1/6b, which is equivalent to b = 6a. We can plug that in and simplify the average to:a + 6a + c/3   We also know that c = 7a, which we can plug directly into the average expression:   a + 6a + 7a/3   = 13a/3 = (13/3)a choice(13/3)a.
<result>C</result>
If a = (1/6)b and c = 7a, then which of the following represents the average (arithmetic mean) of a, b, and c, in terms of a ?