1)http://www.fi.edu/time/keepers/Silverman/html/RomanMatch.html
2) http://www.mathopolis.com/questions/q.php?id=2034&site=1&ref=/roman-numerals.html&qs=2034_2035_2036_2037_2038_2039
3) http://www.softschools.com/math/practice/roman_numeral.jsp
4) http://www.aaamath.com/g4_28wx1.htm#section2
5) http://www.factmonster.com/math/roman-numeral-game.html