Xiaoyun went to the store to buy a pen for the math problem in the second grade of primary school. He bought eight more than two yuan and nine less than two yuan. He asked how much each pen cost.

(2+2)÷(9-8)=4 (Yuan)

Parentheses can be learned step by step: 2+2=4 (yuan) 9-8= 1 (branch) 4÷ 1=4 (yuan).

Supplementary amount: 4×8+2=34 (yuan) or 4×9-2=34 (yuan).

Extended data 1. Generally speaking, the calculation order of the four operations is: if there are brackets, calculate the ones in brackets first; Only the same level of operation, from left to right; Contains two levels of operation, multiplication and division first and then addition and subtraction.

2. Because some calculation problems have their own characteristics, using the algorithm can make the calculation process simple and not easy to make mistakes.

Additive commutative law: a+b=b+a?

Multiplicative commutative law: a×b=b×a

Additive associative law: (a+b)+c=a+(b+c)

Law of multiplicative association: (a×b)×c=a×(b×c)

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