序数词的用法
(1)序数词作定语时，一般要与定冠词或物主代词连用。
eg.Tom is their second son.
He is the first one to come here.
(2)序数词有时可与不定冠词连用，表示数量上又—”,再一”
eg： He tried a second time.他又试了—次。
Shall l ask him a third time?还要我再问他—次吗?我已问了他两次)
(3)序数词的缩写形式为：阿拉伯数字加上这个词的末尾两个字母。
1st 2nd,3rd,4th,20th,21st,22nd,23rd
(4)表示年、月、日时，年用基数词，日用序数词。
2005年8月15日：(英)15,8,2005=15th,August,2005;(美)8,15,2005=August 15th,2005
III基数词和序数词都可以用来给数字编号
The first lesson=Lesson Two(第二课)
第305房间：Room three o(零)five
长安街76号：seventy-six Changan Street
电话号码：204-2244：telephone number two o(零) four two two(double two four four
十一路公共汽车：Bus(No.) eleven
IV 词的表达
分子用基数词，分母用序数词，分子大于1时，分母加s
eg.1/3-one third;2/5-two fifths
V数学运算的表达
eg.3+5=8 Three plus/and five is eight.
9-2=7 Nine minus two is seven.
6x5=30 Five times six is thirty /six unutilized five is thirty.
8÷2=4 Eight divided by two is four.
VI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。
温馨提示：
