Maths F.2

Let R% be the interest rate.

Principal = P
Amount A = 3P
n = 20
R% = ?

A = P(1 + nR%)
3P = P(1 + 20R%)
1 + 0.2R = 3
0.2R = 2
R = 10

Simple interest rate = 10%

我唔知你20年計幾多次息....

我assmue
1. 第一年唔計.... total 19次
2. 計完息之後 入番落銀行

1x (1+R)^19 = 3
1+R = 3^(1/19) ----- 三的開19次方根
1+R = 1.0595
R = 0.0595
R = 5.95%(corr. to 2 d.p.)

Prove
1 x (1+5.95%)^19
= 2.9986 (NEARLY) (OK)

如果計20次息的話
5.6467%


如果唔入番銀行的話
1 + 1x(R) x 19 = 3
= 10.526%

如果唔入番銀行, 又二十次息的話
1 + 1x (R) x20 = 3
20R = 2
R = 10%

(以上R 係利率)