The addition formula is: addend+addend = sum.

Addition represents the number of each known part and what is the sum of the total number relations. It can also be expressed as knowing the sum of one number and another. Generally, it is an addition calculation. The number before the plus sign is called addition, the number after the plus sign is called addition, and the number after the equal sign is called sum. The expression is expressed as addition/arithmetic = sum. If expressed in letters, it is a+b = C.

One-digit addition: When two one-digit numbers are added, the sum can be obtained directly by counting. The result of adding two one-digit numbers is usually compiled into an addition table.

Multi-digit addition: the addition of numbers on the same digit. One number adds up to ten, then go to the previous number and enter one. Multiple digits plus multiple digits, you can first write two multiple digits as the sum of different counting units.

Primary school mathematics:

For mixed operations, if there are no parentheses in the order of mixed operations, multiplication and division are calculated first, and then addition and subtraction are calculated. In the mixed operation with brackets, you should count the parentheses first, and then the parentheses. Observing an object, standing in different positions can see at most three sides of the object at a time. Learning to observe an object can train students' spatial imagination and logical reasoning ability.

Perimeter, the perimeter is the length of a closed figure, the perimeter of a rectangle is twice as wide, and the perimeter of a square is the side length multiplied by 4. Year, month, year has 12 months, February has 28 days in a normal year, 29 days in a leap year, 365 days in a normal year and 366 days in a leap year. Know decimals, read decimals, calculate decimals, and align decimal points when calculating decimal addition and subtraction.