Grade one and grade two arranged addition and subtraction within 20, addition and subtraction within 100, multiplication and division in the table; In the third grade, we arranged addition, subtraction, multiplication and division within ten thousand. The divisor is the multiplication and division of one digit and two digits. In the fourth grade, we arranged addition and subtraction within 100 million. Multipliers and divisors are multiplication and division of three digits, and integers are four operations.

Fraction and decimal cycle:

Get to know it first, and then teach it systematically. The first meeting is arranged in the third grade, and systematic learning begins in the fourth and fifth grades.

(A) the specific arrangement of addition and subtraction operations and internal logic clues

The sequence of integer addition and subtraction: addition and subtraction within 20 (oral calculation)-addition and subtraction of whole ten, whole hundred and whole thousand (oral calculation)-addition and subtraction without carry abdication (written calculation)-addition and subtraction with carry abdication (written calculation)

In the lower grades, I mainly study oral arithmetic, and the composition of numbers has expanded from several ones to dozens, hundreds and thousands. Oral arithmetic teaching is to combine the composition and bit value of numbers, so that students can understand the numbers on the same number and add and subtract directly. On the basis of oral calculation teaching, written calculation teaching allows students to understand the order of vertical calculation and how to align it. This part focuses on the calculation of carry addition and abdication subtraction, and combines the "stick demonstration diagram" in the textbook many times to further let students know how to carry and abdicate. Then the knowledge is analogized to the writing teaching of learning multi-digit addition and subtraction.

5. Teaching of decimal addition and subtraction.

In teaching, teachers' duties are: to help students activate the existing knowledge and experience of integer addition and subtraction, and try to use it to calculate decimal addition and subtraction; Let students know how to align decimal points when the columns are vertical.

6. Teaching of addition and subtraction of scores.

The writing form and arithmetic of fractions are different from integers, which is difficult for students to accept because they need the knowledge of divisibility as the basis. However, the premise of calculation is that the denominator is the same and can be added and subtracted directly.

In short, whether it is integer addition and subtraction, or decimal and fractional addition and subtraction, they all have an inherent and unchangeable main line: they can only directly add and subtract numbers of the same unit. This is just a formality. number