Hindu-Arabic Roman Cardinal Ordinal Ordinal
Symbol Symbol Number Name Number Name Symbol
10 X ten tenth 10th
11 XI eleven eleventh 11th
12 XII twelve twelfth 12th
13 XIII thirteen thirteenth 13th
14 XIV fourteen fourteenth 14th
15 XV fifteen fifteenth 15th
16 XVI sixteen sixteenth 16th
17 XVII seventeen seventeenth 17th
18 XVIII eighteen eighteenth 18th
19 XIX nineteen nineteenth 19th
20 XX twenty twentieth 20th
30 XXX thirty thirtieth 30th
40 XL forty fortieth 40th
50 L fifty fiftieth 50th
60 LX sixty sixtieth 60th
70 LXX seventy seventieth 70th
80 LXXX eighty eightieth 80th
90 XC ninety ninetieth 90th
100 C one hundred one hundredth 100th
400 CD four hundred four hundredth 400th
500 D five hundred five hundredth 500th
900 CM nine hundred nine hundredth 900th
1,000 M one thousand one thousandth 1,000thWhy are the terms cardinal and ordinalsometimes confusedin mathematics?
Cardinal and ordinal numbers are sometimes confused because they have two distinct
mathematical definitions. The cardinal numbers in the numbering system should not
be confused with cardinal numbers in set theory, in which any method of counting
sets using a cardinal number gives the same result. Likewise, the ordinal numbers in
arithmetic should not be confused with ordinal numbers in set theory: Such numbers,
often called ordinals for short, are the order type of a well-ordered set. They are divid-
ed into two types: finite and transfinite ordinals. (For more about sets, ordinals, and
cardinal numbers, see “Foundations of Mathematics.”)