排列组合问题,通常都是以选择题或填空题的形式出现在试卷上,它联系实际,生动有趣;但题型多样,解法灵活。实践证明,备考有效的方法是题型与解法归类,识别模式,熟练运用。下面介绍 Arrangement and combination problems usually appear on the test paper in the form of multiple-choice questions or fill-in questions. It is practical, interesting and interesting; however, the types of questions are varied and the solution is flexible. Practice has proved that the effective method of preparation for examination is the classification of questions and solutions, recognition patterns, and skillful use. The following is introduced