有规律，但是不符合阿基米德定律
序数词 就是在基数词右上头加上th
大部分是基数词在后面加上th变为序数词,但也有特殊情况
①序数词1-9中first,second,third为特殊形式.
②1-19:
first,second,third,fourth,fifth,sixth,seventh,eighth,ninth,tenth,eleventh,twelfth,thirteenth,fourteenth,fifteenth,sixteenth,seventeenth,eighteenth,nineteenth.
③以-ty结尾的基数词,是将y改为i,再加eth.
如:twentieth,thirtieth,fortieth......
④基数词"几十几"变为序数词,只需将个位数变为序数词.
⑤hundred-hundredth,thousand-thousandth....
⑥缩写形式:1st,2nd,3rd,4th,21st,32nd,43rd,54th,65th...
自己找规律,记特殊的.