1数词的分类

一、基数词
 1）基数词写法和读法：345 three hundred and forty-five；
 2）基数词一般是单数形式,但下列情况,常用复数：
 a.与of 短语连用,表示概数,不能与具体数目连 用,如scores of people 指许多人；
 b.在一些表示"一排"或"一组"的词组里；
 如：They arrived in twos and threes.他们三三两两的到达了.
 c.表示"几十岁"；
 d.表示"年代",用 in +the +数词复数；
 e.在乘法运算的一种表示法里,如：3 x 5 = 15 Three fives is (are) fifteen.

 二、序数词
 序数词的缩写形式：first---1st second---2nd thirty-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.