1) The document discusses different number systems including binary, decimal, hexadecimal and negative numbers represented in binary. 2) It explains how to convert decimal numbers to binary and hexadecimal using long division. Negative numbers in binary use the sign-bit method with 1's complement and 2's complement representations. 3) Subtraction in binary is accomplished by adding the normal representation of a positive number to the 2's complement of the negative number. This allows computers to perform subtraction using only addition operations on binary numbers.