XXI. X = 10. XX = 20. I = 1, hence XXI
XXI is the number 21 in Roman numerals.
21 in Roman numerals is XXI. 1 in Roman numerals is I. 90 in Roman numerals is XC. So, 21 1 90 would be XXI I XC in Roman numerals.
The number one is I in roman numerals.
The date 21-11-2007 in Roman numerals would be XXI.XI.MMVII
10 21 1986 in roman numerals: X XXI MCMLXXXVI
A does not have an equivalent in Roman numerals.
The number 49 in Roman numerals is XLIX and the number 99 in Roman numerals is XCIX
The birthday 21-04-1989 in Roman numerals would be XXI.IV.MCMLXXXIX
The number 1999 in Roman numerals is MCMXCIX
The number 638 in Roman numerals is DCXXXVIII
The number 951 in Roman numerals is CMLI
36 I added a link to help you understand how to read Roman numerals.