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.