The Roman numeral for 6 is VI, where V represents 5 and I is 1. When a symbol of lower value appears after a larger-value symbol, the values are added to get the corresponding Arabic number. In this case, VI is 5 plus 1, or 6.
Similarly, when a smaller number precedes a larger number, the numbers are subtracted (IX is 10 minus 1, or 9). Roman numerals are a system of numbers that was used in ancient Rome. Common Roman numerals are I for 1, V for 5, X for 10, L for 50, C for 100, D for 500 and M for 1000.