英文數學功課問題2

1. Let x be the age of the younger brother,
and 27-x be the age of the elder brother
[(27-x)-x]/x = 25/100
(27-2x)/x = 1/4
4(27-2x) = x
108-8x = x
108 = 9x
x = 12
So, the younger brother is 12 years old.

2009-02-05 16:47:49 補充：
可以寫成 "(1+25%)x" 唔好漏左個x

2009-02-05 16:52:19 補充：
其實這題目的解應為:
Let x be the age of the younger brother,
and y be the age of the elder brother
x+y = 27 ---(1)
x(1+25%) = y ---(2)
sub (2) into (1): x+1.25x = 27
2.25x = 27
x = 12

p.s. 設y = 27-x 或 y = (1+25%)x 只是為了簡化題目

2009-02-05 16:55:17 補充：
不好意思 我不喜歡與太多人競爭

2009-02-05 16:58:08 補充：
方法其實差不多

Let x be the age of the younger brother,
and (1+25%)x be the age of the elder brother.
x+(1+25%)x = 27 [total age = 27]
x+1.25x = 27
2.25x = 27
x = 27/2.25
x = 12

2009-02-05 17:03:00 補充：
其他回答者.
在我回答前有多於1個解答的 我便不答 除非回答得不對

Solution:
Let Y be the age of the younger brother. The age of the elder brother is 27-Y.
Y(1+25%) = 27-Y
1.25Y = 27-Y
Y = 12
∴ The younger brother is 12 years old.