Because eight sevens are discharged, it is equivalent to putting seven sevens in each position and putting eight copies in one * * *.

This topic belongs to the category of second-grade mathematics. In the second year, after learning a larger number, the operability was improved. This is the basis of reading and writing large numbers in senior grades, and the particularity of reading 0 should be trained here. After that, there is no knowledge to recite in mathematics study, and it has gradually increased since this semester. Reading and writing methods are one of them. In addition, as the number becomes larger, the corresponding calculation difficulty also increases. The chapter of addition and subtraction not only teaches vertical calculation but also inspires simple quick calculation, and teaches everyone to check the good habits of calculation and lay a good foundation and habits for mathematics in the future.