中一MATH

Let the age of Peter is now x
John is 2 years older than Peter=> John's age=x+2
13 years ago,Peter's age was two-thirds of that of John's
=>(x-13)=(2/3)[(x+2)-13]
=>x-13=(2/3)(x-11)
=>3(x-13)=2(x-11)
=>3x-39=2x-22
=>x=17

So, Peter's age 4 years later=17+4=21

Let x be the age of Peter:(now)
The age of John is (x+2):(now)

(x-13)=(2/3)(x+2-13)
(x-13)=(2/3)(x-11)
3x-39=2x-22
x.......=17

2010-07-15 13:00:37 補充：
To 002:你係唔係曬自己命啊!呢條關奧數咩事,加上你又話自己讀英中,你仲唔係曬命!?

2010-07-16 21:34:08 補充：
17+4
=21

let x be the age of John and y be the age of Peter
x-2=y-------1
(x-13)x2/3=y-13------------2
sub 1 into 2
(x-13)x2/3=(x-2)-13
(x-13)x2/3=x-15
2x-26=3x-45
-26+45=3x-2x
x=19
Therefore,John is 19 years old
Age of Peter
=19-2
=17
Therefore,Peter is 17 years old
使唔使中文版啊

自己讀開奧數的
讀英中的

2010-07-15 12:50:21 補充：
sor...打少左野
peter's age 4 years later
=17+4
=21