1 one first
2 two second
3 three third
4 four forth
5 five fifth
6 six sixth
7 seven seventh
8 eight eighth
9 nine ninth
10 ten tenth
11 eleven eleventh
12 twelve twelveth
13 thirteen
14 fourteen
15 fifteen
16 sixteen
17 seventeen
18 eighteen
19 ninteen
13～19的序数词都是基数词直接加th
20 twenty twentieth
往后,二十几就是twenty加上几,比如23就是twenty-three,序数词twenty-third,其基数词和序数词形式跟前面一样.
30 thirty thirtieth
40 fourty fourtieth
50 fifty fiftieth
60 sixty sixtieth
70 seventy seventieth
80 eighty eightieth
90 ninty nintieth
100 one hundred one hundreth