Concept:Hexadecimal is a base-16 number system that combines symbols used in everyday counting and letters.Explanation:The hexadecimal system has 16 distinct symbols.It uses the decimal digits from 0 to 9.It then uses the letters A to F to represent the values 10 to 15.Thus, hexadecimal numbers are formed by mixing ordinary digits with letters.They are not based on octal or binary symbols alone.Answer:Letters and decimal digits.