单选题
If Mark saved an average (arithmetic mean) of $80 per week for 3 consecutive weeks, how much did he save the second week?
(1)The average amount that Mark saved per week for the first 2 weeks was $60.
(2)The amount that Mark saved the first week was
the amount he saved the second week and 
(1)The average amount that Mark saved per week for the first 2 weeks was $60.
(2)The amount that Mark saved the first week was
the amount he saved the second week and
【正确答案】
B
【答案解析】[解析] (1)中指Mark在前两周中平均每周存60美元，但无法确定第一、二周分别存多少钱；(2)中指出第一周存的钱等于第二周存的钱的[*]，等于第三周存的钱的[*]，设第一周存的钱为x，由题意可得到下面的式子：
[*]
也即Mark第二周存了$80。
[*]
也即Mark第二周存了$80。