What is Number?
A '''number''' is a mathematical object used to '''count''', '''measure''', and '''label''': * People use symbols to represent numbers; they call them [[numeral]]s. Common places where numerals are used are for labeling, as in [[telephone number]]s, for ordering, as in [[serial number]]s, or to put a unique identifier, as in an [[ISBN]], a unique number that can identify a [[book]]. * [[Cardinal number]] * [[Ordinal number]] Numbers are also used for other things like counting. Numbers are used when things are [[measure]]d. Numbers are used to study how the world works. [[Mathematics]] is a way to use numbers to learn about the world and make things. The study of the rules of the natural world is called [[science]]. The work that uses numbers to make things is called [[engineering]]. == Numbering methods == === Numbers for people === There are different ways of giving symbols to numbers. These methods are called [[Numeral system|number systems]]. The most common number system that people use is the ''base 10'' number system. The ''base 10'' number system is also called the [[Decimal|decimal number system]]. The base 10 number system is common because people have 10 [[finger]]s and 10 [[toe]]s. There are 10 different symbols ([[0]], [[1]], [[2]], [[3]], [[4]], [[5]], [[6]], [[7]], [[8]], and [[9]]) used in the base 10 number system. These 10 symbols are called digits.<ref>A finger or a toe is also called a digit.</ref> A symbol for a number is made up of these 10 digits. The position of the digits shows how big the number is. For example, the number 23 in the decimal number system really means (2 times 10) plus 3. Similarly, 101 means 1 times a hundred (=100) plus 0 times 10 (=0) plus 1 times 1 (=1). === Numbers for [[machine]]s === Another number system is more common for machines. The machine number system is called the ''[[binary]]'' number system. The binary number system is also called the base two number system. There are two different symbols (0 and 1) used in the base two number system. These two symbo