"Five,Four,Three,Two,One ...lift off!" is the countdown we hear before a rocket launch.It is a natural for people to count, and we use numbers to do so.The simplest way to represent a number is as a series of marks, or tallies, with each tally representing one item. However, it is difficult to write down or read a very large numbersif it is represented as a collection of tallies.Our own number system, which represents numbers using the digits 0 to 9,enables us to write, read, and manipulate large numbers easily. Arithmetic is the use of numbers in calculations.
We usually use whole numbers to count items such as cakes. However, if only a part of cake is present, we must be a part of a whole number, called a fraction, to count it. Other types of number prove equally useful in different situations.
Number systems
In a place-value number system, the value of a digit in a written number depends on its posotion. In number 22, the 2 on the left is worth ten times more than the 2 on the right.We use a system based on the number 10, but any number can be used as the base for a plase-value system.The ancient Babylonians, for example, used as system based on number 60
