1 one first

r 2 two second

r 3 three third

r 4 four forth

r 5 five fifth

r 6 six sixth

r 7 seven seventh

r 8 eight eighth

r 9 nine ninth

r 10 ten tenth

r 11 eleven eleventh

r 12 twelve twelveth

r

r 13 thirteen

r 14 fourteen

r 15 fifteen

r 16 sixteen

r 17 seventeen

r 18 eighteen

r 19 ninteen

r 13~19的序数词都是基数词直接加th

r 20 twenty twentieth

r

r 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。

r

r 30 thirty thirtieth

r 40 fourty fourtieth

r 50 fifty fiftieth

r 60 sixty sixtieth

r 70 seventy seventieth

r 80 eighty eightieth

r 90 ninty nintieth

r 100 one hundred one hundreth