21 30 31 40 41 50 51基序词和序数词（20 30 40 50 60 70 80 90序数词）

21基数词：twenty-one21序数词：twenty-first30基数词：thirty30序数词：Thirtieth31基数词：thirty-one31序数词：thirty-first40基数词：forty40序数词：fortieth41基数词：forty-one41序数词：forty-first50基数词：fifty50序数词：fiftith51基数词：fifty-one51序数词：fifty-first