The Roman numeral XI stand for the number 11. X is the Roman numeral for 10, and I represents one. In the Roman numeral system, numbers are written as letters arranged in special ways.
Common Roman numerals include V for 5, L for 50, C for 100, D for 500 and M for one thousand. A letter is never used more than three consecutive times in a number. When letters representing smaller numbers precede a letter standing for a larger number, the smaller number is subtracted from the larger one. When, however, letters for smaller numbers follow letters for larger numbers, they are added to the larger one. For instance, 20 equals XX, 30 equals XXX, but 40 equals XL. The ten is subtracted from the 50 to get 40.