Addition and subtraction mixing is a difficult and error-prone point in senior two. The most error-prone places, whether top students or middle school students, will make mistakes because of the wrong operation symbols and careless calculation.

Continuous addition is more difficult than simple addition, mainly because children have to calculate the first part first, and then add the third number to the result. If the child made the first part of the mistake in this process, it would be wrong without this question. Therefore, it is still necessary to emphasize careful calculation and form a good habit of inspection. The same is true for even subtraction. Look at the numbers before you write. There are many careless mistakes, so we directly read the wrong questions. We should try our best to avoid such mistakes.