In the addition formula composed of two addends and summation, the lower grades directly fill the numbers with the addition formula. In middle school, the number of digits has developed from one digit to two digits to multiple digits. Because it is impossible to calculate by mouth, the concept of addition must be used. If the sum of two addends and one of them is known, the calculation of the other addend is based on the calculation method that one addend equals and subtracts the other addend.
Appendix+Appendix = and one addend = and+another addend.
Minus-Minus = difference.
Subtraction = minuend-difference.
Minus = Minus+Difference.
Factor × factor = product.
One factor = product ÷ another factor.
Dividend = quotient.
Divider = dividend quotient.
Dividend = quotient × divisor.
Division with remainder: dividend = quotient × divisor+remainder.
A number is divided by two consecutive numbers. You can multiply the last two numbers first and then divide this number by their product.
The result is the same. Example: 90 ÷ 5 ÷ 6 = 90 ÷ (5× 6).