* Mixed operations arithmetic exercises (second grade, second semester);
Key Points
1. Order of multiplication and division:
If there are multiplication and division in a formula, they should be calculated from left to right; if there are brackets, the numbers inside the brackets should be calculated first, and then the numbers outside the brackets; so, for multiplication and division operations without brackets, if multiplication comes first and division comes later, multiplication should be calculated first, then division; if division comes first and multiplication comes later, division should be calculated first, then multiplication;
Parentheses can be used to change the order of operations, for example: (27 ÷ 9) × 2 and 27 ÷ (9 × 2) have different results;
2. Commutative and associative laws of multiplication:
1 ) Commutative law of multiplication; exchanging the position of factors will not affect the result; for example: 5 × 3 = 3 × 5 = 15;
2 ) Associative law of multiplication; When multiplying multiple numbers, you can multiply any two numbers first, and then multiply another number, for example: (2 × 3) × 4 = (2 × 4) × 3 = 24
