Final answer:
The highest symbol in the hexadecimal system is 'F', which has a decimal value of 15.
Step-by-step explanation:
The decimal value of the highest symbol in the hexadecimal system is 15. In hexadecimal, the system uses base 16, and the symbols range from 0 to F. The symbol 'F' in hexadecimal represents fifteen in decimal. Hexadecimal is often used in computer science and engineering because it corresponds neatly with binary, which is a base-2 system, making it easier for programmers and machines to interpret large binary numbers.