Number bases represent the different methods of expressing numbers. The decimal system is a base-10 system because there are 10 numbers you can use. The binary number system is a base-2 system, because you can only use two numbers (1 and 0). Finally the hexadecimal number system is a base-16 number system. This is because you can use 16 different values as number (1, 2, 3, 4, 5, 6, , 7, 8, 9, A, B, C, d, E, F)