There are different ways of giving symbols to numbers. These methods are called number systems. The most common number system that people use is the "base ten" number system. The "base ten" number system is also called the decimal number system. The base ten number system is common because people have ten fingers and ten toes. There are 10 different symbols {0, 1, 2, 3, 4, 5, 6, 7, 8, and 9} used in the base ten number system. These ten symbols are called digits.