年利率問題.....

利息 = $56875 - $50000
= $6875
本金 x 利率 x 時間 = 利息
設利率是 r
$50000 x r% x 2/1/2 = $6875

125000 x r% = 6875

r% = 6875/125000
r% = 0.055
r = 0.055 x 100
=5.5

∴年利率 = 5.5%

設年利率是a%
50000 x ( 1+a% )2.5次方 = 56875
(1+a%)2.5次方 = 1.1375
2.5log(1+a%) = log 1.1375
log(1+a%) = log 1.1375 / 2.5
(1+a%) = 1.05288
a% = 0.05288
a = 5.29 (取點數後兩位)

2007-01-02 15:43:53 補充：
這是複利息計算

單利息計算

本利和 = 本金 x ( 1 + (年期) (利率) )
56875 = 50000 x (1 + 2.5r%)
1.1375 = 1 + 2.5r%
0.1375 = 2.5r%
r% = 0.055
r% = 5.5%

複利息計算
本利和 = 本金 x ( 1 + (利率) )^(年)
56875 = 50000 x (1+r%)^2.5
1.1375 = (1+r%)^2.5
1+r% = (1.1375)^0.4
r% = (1.1375)^0.4-1