This document discusses different number systems including binary, octal, decimal, and hexadecimal. It provides information on their bases, number of symbols used, and highest value symbol. It also explains how to convert between these number systems and decimal, including most and least significant digits. Steps are given to convert binary to octal and hexadecimal, octal to binary and hexadecimal, and hexadecimal to binary and octal. The document promotes online classes on various ICT subjects for A/L and O/L students being offered in 2020-2021.