求助一道数学题

xiahuistacy

Four extra-large sandwiches of exactly the same size were ordered for m students, where m > 4.  Three of the sandwiches were evenly divided among the students.  Since 4 students did not want any of the fourth sandwich, it was evenly divided among the remaining students.  If Carol ate one piece from each of the four sandwiches, the amount of sandwich that she ate would be what fraction of a whole extra-large sandwich?



答案是4m-12

            ______

            m(m-4)

不好意思 答案选项复制不了 我又不会打分号 所以只能把正确选项发上来 请好心的XDJM指导我 谢谢

zinnia

前三个平分给了m个人，3/m，每个人能得到这么多也是每个人吃的占这3个的比例；最后一个分给了m-4个人，即1/(m-4),每个人能得到这么多也是每个人吃的占这1个的比例；carol每个都分到了，所以她一共吃了的占总共的比例为：3/m + 1/(m-4)，然后同分就是上面答案的形式了。可能表达得不太清楚。。lz想想。。

mydloveal

纠结了半天……原来fourth这里是第四块而不是四分之一……
嗯~4个sandwich 3个平分给m学生 每人3/m Carol也分到了
第4个分给了（m-4）个学生 那么每人1/(m-4) Carol也分到了
那么她吃的就是  3/m + 1/(m-4)=(4m-12)/m(m-4)