Addition

Addition is one of the four basic operations of arithmetic, alongside subtraction, multiplication and division, and is usually written with the plus sign, as in three plus two equals five. It combines two or more numbers into a single total, or sum, and is commutative, so the order of the numbers does not change the result, and associative, so the grouping of numbers being added does not change the result either. Adding zero to any number leaves that number unchanged, which makes zero the operation's additive identity. Addition extends well beyond whole numbers, to integers, real and complex numbers, and abstract objects such as vectors and matrices, and is among the earliest numerical ideas a person learns, with studies finding that infants as young as five months can grasp the basic idea of one plus one.