1, the known minuend is: 20; The known subtractions are: 2; According to the definition of subtraction, the calculated result is: 20-2= 18. So 20-2= 18 is correct.
Two numbers are known: 20 and 2. According to the definition of multiplication, the calculation result is: 20×2=40. So, the product of 20 and 2 is 40.
Related knowledge of formulas
1. In mathematics, expressions refer to expressions listed when calculating numbers (or algebraic expressions), including numbers (or letters instead of numbers) and operation symbols (four operations, powers, roots, factorials, permutations and combinations, etc. ). According to the different calculation methods, the formulas are generally divided into horizontal and vertical.
2. Unlike expressions, expressions are expressions that connect data of the same type (such as constants, variables, functions, etc.). ) Use operation symbols according to certain rules. Expressions are expressions that connect numbers through operation symbols to calculate results, and need an equal sign.
3. Expression refers to the expression used in the operation between numbers. Usually composed of mathematical symbols, numbers and operational symbols, it is used to express the relationship and structure of mathematical operations. Formulas can be divided into simple formulas and complex formulas according to their expressions and complexity.
4. Simple expressions refer to expressions composed of basic operation symbols such as addition, subtraction, multiplication and division. These simple expressions include basic operations such as addition, subtraction, multiplication and division, as well as basic operation symbols such as brackets and powers.
5. Complex expression refers to an expression composed of multiple simple expressions, including multiple simple expressions and basic operation symbols such as parentheses and power sum operation sequence. When calculating the formula, we should pay attention to the following points: master the basic operation rules: the rules and order of basic operations such as addition, subtraction, multiplication and division, and the use of brackets and idempotent basic operation symbols.
6. Pay attention to the order of operations: in complex formulas, it is necessary to pay attention to the order and priority of operations, and calculate in the order of first power, then multiplication and division, and then addition and subtraction, and pay attention to the priority in parentheses.
7. Check symbols and numbers carefully: check the accuracy of symbols and numbers during calculation to avoid mistakes. Keep clear thinking: pay attention to clear thinking when calculating, and clarify the purpose and method of calculation to avoid confusion and mistakes.