First of all, it is necessary to distinguish between combination and arrangement. If it is a combination, it cannot be arranged. Pay attention to the back row when solving problems. If you don't arrange it, you can't arrange it, otherwise it will be repeated. Quote "Six people are divided into three groups on average. Multiply C64 by C42 by C22. Finally, if there is duplication, divide it by A33, that is, how many groups you are divided into, divide it by A but divide it equally. " Because it is divided into three groups on average, and these groups are equivalent! X×A33=C64×C42×C22, so X= 15. However, if it is divided into three parts: A, B and C, then these groups will be arranged! The previous x is out of order, so the result of this calculation does not need to be divided by A33. For example, it is still divided into three groups, but this time it is a group of three people, a group of two people, 1 person. Although there are no groups A, B and C, the number of elements in each group has changed! In fact, there are three different groups, and the relationship is not equivalent, so this one should also be ranked, and the answer need not be divided by A33.