代數問題(5)，數學達人請進。

Let the speed of finishing the model by 軍曹be x s^-1
and the speed of finishing the model by 夏美 be y s^-1

As the amount of work is the same for anybody,
so 5x = 3.5 (x + y)
5x = 3.5 x + 3.5 y
1.5 x = 3.5 y
x = 7y/3

若夏美獨自去砌的話，需時= 5x/y s
= 5 (7y/3)/y s
= 35/3 s

2010-09-08 13:10:21 補充：
Sorry that I made some errors...
please see the revised steps:

Let the speed of finishing the model by 軍曹be x hour^-1
and the speed of finishing the model by 夏美 be y hour^-1

As the amount of work is the same for anybody,
so 5x = 3.5 (x + y)
5x = 3.5 x + 3.5 y
1.5 x = 3.5 y
x = 7y/3

2010-09-08 13:10:26 補充：
若夏美獨自去砌，需時= 5x/y hour
substitute x = 7y/3 into 5x/y,
夏美需時
= 5 (7y/3)/y hour
= 35/3 hour

The unit of 001'ans should be hour but not second

軍曹砌一小時高達模型可完成1/5
軍曹+夏美砌一小時高達模型可完成1/3
所以夏美砌一小時高達模型可完成
=1/3-1/5
=2/15
所以若夏美獨自去砌的話，需時
=1/(2/15)
=15/2小時 or 7.5小時

2010-09-05 10:14:30 補充：
對不起 看錯了 原來是3.5小時
所以軍曹+夏美砌一小時高達模型可完成1/3.5
所以夏美砌一小時高達模型可完成
=1/3.5-1/5
=3/35
所以若夏美獨自去砌的話，需時
=1/(3/35)
=35/3小時 or 11又2/3小時