Q10:

A total of $60,000 was invested for one year. Part 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 =3y/4

(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.

答案为什么是C不是Ｄ？

要知道总的利息就要知道,2个利息的比和分别有多少钱放在2个利率的户头里.缺一不可.

4080=A*x%+(6000-A)*y%

有3个未知数，必须有3个方程才能求解，也就是说必须再有2个方程才行。

单单知道

条件1：x =3y/4

或者

条件2：A/(6000-A)=3/2

都是不够的，必须1+2合起来才能求出答案！选C