问题
问答题
Over the last three years a scientist had an average (arithmetic mean) yearly in come of $45,000. The scientist earned 1 
times as much the second year as the first year and 
times as much the third year as the first year. What was the scientist’s income the second year ？
答案
参考答案：
40,500美元。
解析：
设这位科学家第一年的收入为x美元，根据题意可得：
[*]
所以他第二年的收入为[*]40,500美元