问题
单项选择题
If the average (arithmetic mean) of a and b is 110, and the average of b and c is 160, what is the value of a-c ？（）
A. -220
B. -100
C. 100
D. 135
E. It cannot be determined from the information given.
答案
参考答案：B
解析：
Restate both statements as equations: a+b=220 and b+c=320. Subtract the second equation from the first and you get a+b-b-c=220-320=a-c=-100.