Last semester, the students have learned the practical problem of how much is left after removing a part from the total. This semester, they have learned how much is original and how much is practical. On this basis, guide them to find the practical problem of the difference between two numbers. It is difficult for students to understand the quantitative relationship. So after this lesson, they were deeply touched.

1. Constantly improve the understanding of the practical problem of the difference between two numbers in different expressions.

Teaching examples, students through hands-on operation, group cooperation, active observation and comparison, on this basis, let students fully discuss, and then express their views, speak freely, through induction, a preliminary unified understanding. In operation, the students' method is to compare the two colors of flowers after aligning and discharging, which can quickly find the difference and draw the formula smoothly, but the students' understanding of the practical problem of how much the two numbers are different is not in place. Just to sum up: number is the result of comparing two numbers, and it is done by subtraction. Here I draw 13 and 8 circles on the blackboard with the simplest way-blackboard writing, and use the corresponding colors to represent red and blue flowers. By using the outline, dotted line and question mark, the meaning of the question is simple and clear, especially students can clearly find that "8" can not only represent the number of blue flowers. Immediately show the eight red flowers subtracted from the picture, and the students quickly understand the true meaning of "how much is the difference between two numbers" Of course, subtraction is used to "divide", and it is clear from the root why subtraction is used to "how much is the difference between two numbers". The child who realizes this has a real and sweet smile on his face. Then ask: how to make two kinds of flowers as many? what do you think? What students think of is to go more and add less. Using blackboard operation, students find that the same quantity has changed from an intuitive picture to an abstract formula, that is, the difference between two numbers, and their understanding of the practical problem of how big the difference is has become full. Students understand the different expressions of the same method and find out the difference between two numbers, which consolidates and enriches the significance of subtraction in time and helps them to think from one to another in the future.

2. Pay attention to the consistency of mathematics learning

This lesson studies the practical problem of the difference between two numbers. Practice and consolidation are all around this type, so students all use subtraction to solve problems. When teaching examples, students are required to ask questions according to two conditions, and naturally there are two types. After explaining the category of "finding the difference between two numbers" in various ways, we can better communicate the relationship between the two quantities and consolidate new knowledge and experience by comparing it with the practical problem of how much the sum of two numbers is learned before.