重复与遗漏是学生解排列组合应用题最易出现的错误之一.究其原因除了思考方法特殊之外,更重要的是由于重复与遗漏问题多出现在“特殊元素与特殊位置”这种复杂的题型中.这类题型往往出现:①几个元素受同等条件的限制;②某个元素受多种条件 Repetitions and omissions are one of the most common mistakes that students make in structuring combinatorial problems. The reason is that in addition to the special way of thinking, it is more important that the problems of repetition and omission appear in the complex of “special elements and special positions”. In the question type, such question types often appear: 1 Several elements are restricted by the same conditions; 2 Some element is subject to various conditions