Why 9 distinct equal number symbols?

It is because the number system is decimal(10 based).(there are actually 10 distinct numbers including 0). In binary number system there is only two distinct number 0 and 1, and things starts again once you reach counting 1. That is 0,1,10,11 in binary are equivalent to 0,1,2,3 in decimal. Similarly, in octal number system there are 8 distinct numbers and so is 16 in hexadecimal number system. So it is the number system which determines how many distinct numbers will be there.