二、序数词
序数词的缩写形式： first——1stsecond——2ndthirty-first——31st
三、 数词的用法
1)倍数表示法
a. 主语+谓语+倍数(或分数)+ as + adj. + as
I have three times as many as you.我有你三倍那么多。
b. 主语+谓语+倍数(分数)+ the size (amount，length…) of…
The earth is 49 times the size of the moon.地球是月球的49倍。
c. 主语+谓语+倍数(分数)+ 形容词(副词)比较级+ than…
The grain output is 8 percent higher this year than that of last year.
今年比去年粮食产量增加8%.
d. 还可以用by+倍数，表示增加多少倍
The production of grain has been increased by four times this year.
今年粮食产量增加了4倍。
2)分数表示法
构成：基数词代表分子，序数词代表分母。分子大于1时，分子的序数词用单数，分母序数词用复数：
1/3 one-third ; 3/37 three and three-sevenths.