单选题
If a + 2b = 14 and 5a + 4b = 16, what is the average (arithmetic mean) of a and b?
(A) 1.5
(B) 2
(C) 2.5
(D) 3
(E) 3.5
【正确答案】
C
【答案解析】Use TACTIC 6: don't do more than is necessary. You do not need to solve this system of equations; we don't need to know the values of a and b, only their average. Adding the two equations, we get 6a + 6b = [*]