"Multiplication characteristics of 3" is the content of Unit 3 in the first volume of the fifth grade of mathematics published by Beijing Normal University, which belongs to the field of "number and algebra". It is based on the understanding of integers, four operations of integers, factors, multiples, multiples of 2 and 5, and is an important basis for finding the greatest common factor and the smallest common multiple. In order to let students learn and discover the rules more independently, the author has made great adjustments in the teaching design: the learning materials are changed from hundreds of tables to groups. Students find it difficult to find the law from the front in the process of exploring the multiple characteristics of 3, but more are negatively transferred by the multiple characteristics of 2 and 5. Taking group numbers as students' learning materials can better focus students' exploration on the characteristics of numbers, so as to discover and understand the laws.

Characteristics of multiples of 3: If the sum of digits of a number is a multiple of 3, then this number must be a multiple of 3. 1, an integer can be divisible by another integer, and this integer is a multiple of another integer. For example, 15 can be divisible by 3 or 5, so 15 is a multiple of 3 and 5. 2. The quotient obtained by dividing one number by another. For example, a÷b=c, that is, A is a multiple of B, for example, A÷B=C, it can be said that A is c times of B. 3. A number has countless multiples, that is to say, the set of multiples of a number is an infinite set.