is a branch of mathematics
which records elementary properties of certain operations
The traditional operations are addition
although the more advanced operations, exponentiation
and square roots, are also a part of this subject. Arithmetic is performed according to an order of operations
The arithmetic of natural numbers, integers, rational numbers (in the form of fractions) and real numbers (in the form of decimal expansions) is typically studied by schoolchildren of the elementary grades. Representations of numbers in terms of percentages are generally studied then as well. However, in adult life, most people rely on calculators to perform arithmetical computations.
The term "arithmetic" is also used to refer to elementary number theory; it's in this context that one runs across the fundamental theorem of arithmetic and arithmetical functions.