672-36+64=672+4-36+60=676-36+60=640+60=700。 Additive commutative law: When two numbers are added, the sum of the positions of the addends remains the same, and the letter a+b=b+a is used. Law of addition and association: when three numbers are added, the first two numbers are added, or the last two numbers are added first, and the sum is unchanged, which is expressed by letters: (a+b)+c=a+(b+c).

Subtraction property 1: a number, two numbers are subtracted continuously, and the position of subtraction is exchanged, and the difference is unchanged, which is expressed in letters: a-b a-b-c = a-c-b c-B. Subtraction property 2: a number subtracts two numbers continuously, which is equal to subtracting the sum of these two subtractions. Use letters to represent a-b-c=a-(b+c). The properties of addition and subtraction operations are expressed by letters: a+b-c = a-c+b, a-(b-c) = a-b+c, and a-(b+c) = a-b-c.

In the first grade of primary school, there is addition and subtraction within 100 in the mathematics stage of primary school. There are ten methods. This requires children to practice more. As long as the first-year students master the calculation method, other calculation problems will be solved. Split and addition of integers; For example; 8+5 = 13, first split "5" into "2" and "3"; Then it is 8+2+3 = 10.