If x dollars are invested at 12 percent for one year and y dollars are invested at 8 percent for one year, the annual income from the 8 percent investment will exceed the annual income from the 12 percent investment by $64. If $5,000 is the total amount invested between x and y, how much is invested at 12 percent ？（）
A. $1,680
B. $1,997
C. $3,003
D. $3,320
E. $3,500
参考答案：A
解析：
From the information in the question, you can set up the equation 0.08y=0.12x+64; to get rid of the decimals, you can multiply both sides by 100 and get 8y=12x+6,400, which can be restated as 2y-3x=1,600. From the information in the question, you can also set up the equation y+x=5,000, which can be restated as 3y+3x=15,000; if you add the two restated equations together, you will get 5y=16,600; y=16,600/5=3,320. If 3,320+x=5,000, then x=1,680.