1到30的序数词为: 1st = first 2nd = second 3rd=third 4th=fourth。 5th=fifth 6th=sixth 7th=seventh 8th=eighth。 9th=ninth 10th=tenth 11th=eleventh 12th=twelfth。 13th=thirteenth 14th=fourteenth 15th=fifteenth 16th=sixteenth。 17th=seventeenth 18th=eighteenth 19th=nineteenth 20th=twentieth。 21st=twenty-first 22nd=twenty-second 23rd=twenty-third 24th=twenty-fourth。 25th=twenty-fifth 26th=twenty-sixth 27th=twenty-seventh 28th=twenty-eighth。 29th=twenty-ninth 30th=thirtieth。 扩展资料: 序数词的用法 1、当序数词前有形容词性物主代词或名词所有格修饰时,序数词前不用the。 2、当表达分数时,序数词前不用the。 3、当表达“又一,再一”时,序数词前不用the,但可加不定冠词。 4、当表达“年月日”时,序数词前不用the。 5、当序数词在句中作状语时,序数词前不用the。 6、当表达考试(赛跑等)中获得的名次时,序数词前不用the。 7、示某人的多少岁生日时,序数词前不加the。