In essence, it is to investigate the operation of addition, subtraction, multiplication and division. Addition, subtraction, multiplication and division are the basic four operations, and the symbols are "+-×" in turn. Without parentheses, the operation order is multiplication and division first, then addition and subtraction. +is a plus sign, the numbers before and after the plus sign are addends, = is an equal sign, the number after the equal sign is a minus sign, the minus sign is a minuend, and the number after the equal sign is a difference. "×" is a multiplication sign, the numbers before and after the multiplication sign are called factors, "=" is an equal sign, the number after the equal sign is called product "∫" is a division sign, the divisor is before the division sign, and the number after the equal sign is a quotient. Those with the same calculation results are divided into the same group.