Addition (usually indicated by the plus sign "+") is one of the four basic arithmetic operations, and the others are subtraction, multiplication and division. For example, * * * has a combination of three apples and two apples, and * * * counts as five apples. This observation is equivalent to the mathematical expression "3+2 = 5", that is, "3 plus 2 equals 5".

Law of addition:

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

Multi-digit addition: add the numbers on the same digit, which digit adds up to ten, and then enter one to the previous digit.

Multiple digits plus multiple digits, two multiple digits can be written as the sum of different counting units, and then the numbers of the same counting unit are added respectively according to the addition algorithm and the addition rule of one digit.