一、二、三,單獨記；八去t,九除e,ve要用f替,整十基數(shù)變序數(shù),先把ty變成tie；要是遇到兩位數(shù),十位基數(shù)個位序,th最后加上去.
解析口訣：one→first,two→second,three→third這三個詞變化特殊,要單獨記；eight→eighth,nine→ninth,八去t,九去e后再加-th； five→fifth,twelve→twelfth,五、十二把ve換成f再加-th；twenty→twentieth,thirty→thirtieth...整十先把詞尾y改為ie再加-th.兩位數(shù)時則十位數(shù)用基數(shù)詞,個位數(shù)用序數(shù)詞,如：twenty-first.