GWD7-29

[Martina]

Q29:
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.

Ans: C

這題要麻煩大家嚕!! 不知道有沒有人問過 .......

[homaru]

設一部份A, 利率x%, 一部份60000-A, 利率y%
A*x% + (60000-A)*y%=4080

條件1,知道x跟y的比例3:4 (設x=3n, y=4n)
條件2,知道A*x% 跟 (60000-A)*y% 的比例3:2
聯立 A*3n% : (60000-A)*4n% = 3:2
3A : 4*(60000-A) = 3:2
A=40000
代入原式子可求得x