A number is a mathematical object most commonly used for counting and measuring. Originally, whole numbers or integers will have been used to count objects. Over time, the system has been extended to include more numbers which turned out to be useful. The extensions include zero and the negative numbers, non-integers (or numbers that are not whole numbers) that can be expressed as fractions or decimals. All numbers on the real number line are either rational or irrational. Number basics are covered in the following lessons: