MATH(英)f.2

Let the original amount of money be $y, r be the time required

y((10*r)/100)+y=3y
(0.1r+1)y=3y
0.1r+1=3
0.1r=2
r=20

It needs 20 years to treble the amount of money.

2007-08-15 00:31:47 補充：
y((10*r)/100) is the total amount of simple interest in r years;y is the original amount of money3y is the sum of money after r years( treble of the original amount of money).∵數式左右兩邊的y可以抵銷，∴不用計算金錢的真實值。

2007-08-19 22:10:04 補充：
p.a.=per annual，即每一年10%p.a. 5＝10%every year，兩者無分別