Addition is the mathematical operation that combines two or more numbers to produce their sum.
For simple addition of whole numbers, it is easy to add by counting steps. If we consider 6 + 4, then we can start at 6, then add 1 four times: 7, 8, 9, 10. Thus, 6 + 4 is 10.
For more complex addition, long addition can be carried out.
Addition is commutative, thus a + b = b + a.
Formal definition
It is helpful to see addition in terms of functions - addition adds one number (a) to another number (b) to make their sum (c).
Thus,
a + b = c.
Its reverse function, or inverse operation, is subtraction, which moves the other way:
c - b = a.
It is possible to add a negative number, but this is the same as subtracting that number:
a + (-b) = a - b.