How to make children understand the relationship between addition and subtraction?

Some parents asked: When the child is doing exercises, can she calculate the number in her heart? She asked her how to calculate the formula. She doesn't quite understand. In other words, when calculating the formula, she doesn't know whether to add or subtract. How can I tell her to understand? Let's look at the specific topic:

The term 1 contains two subtraction formulas, in which the condition of "everyone writes 15 big characters" is used twice. When practicing, let the children talk about what they know after reading the questions, and make the questions and conditions clear. The required question is the last calculated number, which should be written on the right side of the equal sign. The problem is to find the total, using addition, and the problem is to find the partial number, using subtraction. After analyzing the topic, we know that the Chinese character 15 written by everyone is a * * * Chinese character to be written, which is the total. Divided into two parts: what has been written and what needs to be written. The left side needs to be written, and the sum part needs to be written. Subtract the total 15 to write seven. On the right, I wrote a few questions, which are also the part of seeking. I need to write 6 less from the total 15. I want to strengthen the contrast between the two questions and let the children talk about the different places. For children who don't understand, it is suggested that children make a pendulum with a stick or draw a picture on the manuscript paper, so that children can intuitively see the relationship between the total number and the partial number.

The second and fourth questions are subtraction with redundant conditions, and the redundant conditions of the second question are written next to them. It is easy for children to find the time. The redundant conditions and useful conditions in the fourth question are written together, and they are all about the number of people, so it is difficult to distinguish them. Let children carefully analyze the relationship between conditions and problems and eliminate unnecessary conditions.

Parents can make full use of the exercise materials provided in question 4 to guide their children to learn how to analyze problems. This includes two aspects: first, starting from the problem, looking for suitable conditions. The question is how many people are hiding. Needless to ask this question, the total number of people playing hide-and-seek should be 14 MINUS 6 people outside and 20 people in the class. Second, starting from the conditions, see which two conditions are related, which questions can be raised, which questions are required in the topic, and which two conditions are chosen to solve the problem. There are 20 people in the class, 14 are playing hide and seek. How many people are not playing hide and seek? This obviously does not meet the problem. Look at 20 people in the class and 6 people outside. Can you ask some questions? No, the number of people in the class MINUS the number of people outside will not equal the number of people inside, because some people have not participated in hide-and-seek yet. Finally, we can only choose "there are 14 people playing hide-and-seek" and "there are 6 people outside" and ask "how many people?"