The arithmetic rules in primary school mathematics are: additive commutative law, the law of addition and association, the nature of subtraction, the law of multiplication and exchange, the law of multiplication and association, the law of multiplication and distribution, and the nature of division. These algorithms apply to integers, decimals, fractions and percentages. Among them, multiplication and division is the most important of these algorithms, and it is also difficult for students to master.

1. additive commutative law: Two numbers are added, the position of the addend is exchanged, and the sum is unchanged. Expressed in letters: a+b = b+a.

Example 40+56=96 56+40=96

So 40+56=56+40

Second, the law of addition and association: when three numbers are added, the first two numbers are added first, or the last two numbers are added first, and the sum is unchanged.

Expressed in letters: (a+b)+c=a+(b+c)

Example 88+104+96 88+104+96

=(88+ 104)+96 =88+( 104+96)

= 192+96 =88+200

=288 =288

So (88+104)+96 = 88+(104+96)

Additive commutative law and additive associative laws can be used simultaneously.

Example:115+132+118+85.

=115+85+132+118 ... additive commutative law

= (115+85)+(132+118) … additive associative law.

=200+250

=450

Third, the essence of subtraction.

If a number subtracts two numbers continuously, the sum of these two numbers can be subtracted; You can also subtract the first subtraction and then the second subtraction, and the result remains the same. Expressed in letters: a-b-c=a-(b+c)

Example 234-66-34 234-66-34 234-66-34

= 168-34 =234-(66+34) =234-34-66

= 134 =234- 100 =200-66

= 134