“放球入盒”问题可以分为两类.一n个不同的小球放入m个不同的盒子里例17个不同的小球放入7个不同的盒子里,有几种不同的放法?分析:先将7个小球全排列,然后依次将小球装入7个盒子里,共有A77=7!种.不能同时将球和盒子都作全排列,因为将球全排列后,每个盒子都有可能装到每个小球. The problem of “putting the ball into the box” can be divided into two categories. One n different balls are put into m different boxes, 17 different balls are put into 7 different boxes, there are several different puts. Method analysis: first arrange all seven balls, then put the balls into seven boxes in order, total A77=7! kind. You can’t make all the balls and boxes at the same time because the balls are all arranged. Each box has the potential to fit into each ball.