The document discusses decimal and hexadecimal number systems. The decimal system uses 10 symbols (0-9) in a positional notation where the value of each digit depends on its position. Hexadecimal uses 16 symbols (0-9 plus A-F) with a base of 16. To convert between number systems, the integer and fractional parts are converted separately by repeated division or multiplication by the new base. For example, to convert decimal 765.245 to hexadecimal, 765 divides into 16 with remainder 13 and fractional part 0.245 is multiplied by 16 repeatedly.