ANSWER: 4m-12 / m(m-4)

  我是这么理解的：4块很大的三明治，m个学生分（m>4) ， 3个是m各学生平均分，1个是m-4个学生分 Carol 四个三明治 每个都吃一块 他吃的站总共三明治的多少

 难道是我理解错了 Carol 吃了4块啊 总共不就是 3m+(m-4）么 怎么出来的那个式子

 多谢执教

慢慢來看, 不难的.

Three of the sandwiches were evenly divided among the students
= 3cakes/m (每个student分到的量)

the fourth sandwich was evenly divided among the remaining students
= 1cake/(m-4) (剩下student分到的量)

 If Carol ate one piece from each of the four sandwiches
= Carol有吃了4块, 所以她吃到的量是 3cakes/m + 1cake/(m-4)

the amount of sandwich that she ate would be what fraction of a whole extra-large sandwich
= [3cakes/m + 1cake/(m-4)]/ (4cakes) --单位可消掉
= (4m-12)/ m(m-4)