嘉健帶了若干零用錢上街，他先利用一半零用錢買兒童雜誌，然後再用19元購買一個套餐，最後餘下2元。問嘉健原來有多少零用錢呢

設健原來有零用錢n元
n/2-19 =2
n/2-19+19=2+19
n/2x2 =21x2
n =42

如果一般
(2+19)x2
=21x2
=42

我唔係幾識用中文去寫﹐用英文ok嘛﹖

Let $x be the amount of Ka Kin have

Sol : x/2 - 19 = 2 ← x/2 = 二分之x= x 除二
x/2 = 2+19
x = 21x2
x = 42//

Therefor, Ka Kin have $42 dollars.

設原有y元
y/2-19=2
y/2 =2+19
y =21*2
y =42
嘉健原來有42元零用錢

答案係42元
個式係
19+2乘2
意思姐係用左一半既錢仲有21元
咁姐係原有要42蚊囉

嘉健原來有
(19+2)/(1/2)
=21*2
=42(元)