The document discusses the decimal and binary number systems. It explains that computers use binary, which represents numbers as sequences of 0s and 1s, because their internal workings are based on two states of electricity - on or off. It then shows how to convert between decimal and binary, and how to perform arithmetic operations like addition, subtraction, multiplication and division in binary. Some examples of these binary operations are provided. Finally, it gives some practice problems to convert between decimal and binary, and perform binary arithmetic.