In computer system, subtract, add, divide and multiple is not done as arithmetic way. It is performed by the technique that is called Complement.
1`s complement and 2`s complement
9`s complement and 10`s complement
Number system refers to the base, arrangements and positional value of digits in number system. Simply, its a way to represent numbers. It is of 4 types; Binary, Decimal, Octal and Hexadecimal number system.