The value of a number is the sum of the positional values of its digits. In an additive number system, the value of a written number is the sum of the face values of the symbols that make up the numbe...The value of a number is the sum of the positional values of its digits. In an additive number system, the value of a written number is the sum of the face values of the symbols that make up the number. If a symbol to the left was smaller than the symbol to the right, it would be subtracted instead of added. In the mixed base system, instead of powers of 10, numbers are broken down into sums of numbers that look like 4 times a power of 10 (40, 400, 4000, etc.).