why use the decimal system?

The most likely answer is the simplest.That also explains why the Aztecs used a base 20, or vigesimal system.But other bases are possible, too.Babylonian numerals were sexigesimal,or base 60.Any many people think that a base 12,or duodecimal system,would be a good idea.Like 60, 12 is a highly composite number that can be divided by two,three,four,and six,making it much better for representing common fractions.