“两位数加一位数（进位）”是在２０以内进位加法和整十数加两位数的基础上进行学习的，其算理和算法与不进位加法完全相同，是旧知识的延伸和发展。因此，对这种新旧联系密切的知识，关键要以旧引新，使学生把原有的知识类推、迁移到新知识的学习上，培养学生运用旧知识探索? The “double-digit plus one-digit (carry)” is learned on the basis of carry-on additions and whole-number plus two-digit numbers within 20, and the arithmetic and algorithm are exactly the same as the non-carry addition and are an extension of the old knowledge And development. Therefore, the close connection between the old and the new should be based on the old principle of introducing new knowledge so that the students can transfer the original knowledge to the new knowledge and cultivate the students to use the old knowledge to explore.