Q19:

A total of $60,000 was invested for one year.  But of this amount earned simple annual interest at the rate of x percent per year, and the rest earned simple annual interest at the rate of y percent per year.  If the total interest earned by the $60,000 for that year was $4,080, what is the value of x?

(1)     x = (3/4) y

(2)   The ratio of the amount that earned interest at the rate of x percent per year to the amount that earned interest at the rate of y percent per year was 3 to 2.

给出来的答案是C,我觉得是D呢？迷惑……

ax+(60,000-a)y=4080

x=(3/4)y

ax/[(60,000-a)y]=3/2

答案是C

题干中一共有3个未知数：x,y和the amount at the rate of x%

单单一二都只能解决一个未知数，只有1+2时，才能解出x