优质解答
把每个人起一个名字,分别叫1,2,3,4,5.
中间一个不变,假若同学3 始终站在中间,则中间一个不变的站法有：
12345,12354,14325,14352,15324,15342,
21345,21354,24315,24351,25314,25341,
41325,41352,42315,42351,45312,45321,
51324,51342,52314,52341,54312,54321.共24种站法.
方法二：依据分步计数原理就是：4x3x2x1=24.
把每个人起一个名字,分别叫1,2,3,4,5.
中间一个不变,假若同学3 始终站在中间,则中间一个不变的站法有：
12345,12354,14325,14352,15324,15342,
21345,21354,24315,24351,25314,25341,
41325,41352,42315,42351,45312,45321,
51324,51342,52314,52341,54312,54321.共24种站法.
方法二：依据分步计数原理就是：4x3x2x1=24.