1, transverse formula:
2+ 1 1-9=4
4- 1x0=4
2+7-5=4
2. Vertical formula:
2+4÷2=4
1 1- 1x7=4
9-0-5=4
definition
Addition: the operation of combining two numbers into one number.
Subtraction: when two addends and one of them are known, the operation of finding the other addend.
Multiplication: the operation of finding the product of two numbers.
Division: the operation of finding another factor by knowing the product of two factors and one of them.