有D數學題不懂，如可答，有10點！

Let the compound interest rate be r%.

There are 2 half years in 1 year.

3800 ( 1 + r% / 2 )^2 - 3800 = 389.5

3800 ( 1 + r% / 2 )^2 = 4189.5

( 1 + r% / 2 )^2 = 1.1025

1 + r% = 1.05

r% = 0.05

r = 5

Hence the interest rate p.a. is 5%.


2007-07-25 20:45:33 補充：
Sorry that I have forgotten the r% / 2 and so the answer should be 10%.

Let the compound interest rate be r%. For half-yearly compound interest, the number of periods per year is 2. So we can set the equation
3800 * (1 + r% / 2) ^ 2 - 3800 = 389.5
(1 + r/200)^2 = (389.5 + 3800) / 3800 = 1.1025
1 + r/200 = sqrt(1.1025) = 1.05
r = (1.05 - 1) * 200 = 0.05 * 200 = 10
Therefore, the compound interest rate per annum is 10%.