✔ 最佳答案
1. 設本金 = x
x * (1+5% * 3) = 4140
x * 115% = 4140
x = 4140 / 115%
x = 3600
2. 設其中一份投資為 y 元, 則另一份投資為4500 - y
y * 10% = (4500 - y) * 8%
0.1y = 4500 * 8% - 0.08y
0.1y + 0.08y = 360
0.18y / 0.18 = 360 / 0.18
y = 2000
所以其中一份投資為 2000 元, 則另一份投資為4500 -2000 = 2500 元
3. 設本金為y元, 年數為 n
y * (1+ 5%*n) = 2y
(1+ 5%*n) = 2
1 + 5%*n - 1 = 2 -1
5%+n = 1
n = 1 / 5%
n = 20
所以共需20 年
2008-11-29 20:50:27 補充：
5. 剛智將$80000存入銀行，每3個月計算複利息一次，存款半年後可得利息$2418。求年利率
設年利率為r%
80000 * (1 + r%/4)^2 - 80000= 2418
80000 * (1 + r%/4)^2 = 2418 + 80000
(1 + r%/4)^2= 82418 / 80000
(1 + r%/4)^2 = 82418 / 80000
(1 + r%/4)^2 = 1.030225
1 + r%/4 = 1.015
r%/4 = 1.015 - 1
r% = 0.015 *4
r = 0.06*100
r= 6
