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