簡單方程~~~~~~~~

設x為小明今個月的零用錢
(1-1/5)x = 72
(4/5)x = 72
x= (72*5)/4
x=90 (元)

答: 小明今個月的零用錢有90元

Let's x=小明的今個月的零用錢

72/1/5
=72*5
=360

2008-02-19 20:32:07 補充：
sorry ,that answer is incorrect,this is correct:72/(1-1/5) =72*5/4 =90

設他今個月有零用錢y元。

(1-1/5)y = 72
4/5y = 72
4/5y÷4/5 = 72÷4/5
y =72x5/4
y =90

他今個月有零用錢90元。