数词分基数词和序数词。基数词表示数目,序数词表示顺序。
1. 基数词的用法
(1) 基数词在句中主要用作主语、宾语、定语、表语、同位语,例如:
Thirty of them are Party members. (主语)
--- How many would you like ?
--- Three , please .(作宾语)
The nine boys are from Tianjing. (定语)
Six plus four is ten. (表语)
We four will go with you. (同位语)
(2) 表示一个具体数字时, hundred, thousand, million 一律不用复数;在表示一个不确定数字时则用复数。例如:
Our country has a population of 1,300 million people.
There are three thousand students in our school.
After the war, thousands of people became homeless.
Maize is the most important food crop for millions of people in the world.
They arrived in twos and threes .
(3) 表示 “…… 十 ” 的数词的复数形式可用来表示人的岁数或年代,例如:
He is in his early thirties. He died still in his forties. This took place in 1930s.
(4) 表示时刻用基数词。例如:
We get up at six. The workers begin work at eight.
表示 “ 几点过几分 ” ,用介词 past, 但须在半小时以内。例如:
ten past ten, a quarter past nine, half past twelve
表示 “ 几点差几分 ” 用介词 to, 但分数须在半小时以上。例如:
twenty to nine, five to eight, a quarter to ten
表示 “ 几点几分 ” 还可直接用基数词。例如:
seven fifteen, eleven thirty, nine twenty
2. 序数词的用法
(1)序数词主要用作定语,前面要加定冠词,例如:
The first truck is carrying a foot baskets. John lives on the fifteenth floor .
(2)序数词有时前面可加不定冠词来表示 “ 再一 ” , “ 又一 ” 这样的意思,例如:
We'll have to do it a second time. Shall I ask him a third time?
When I sat down, a fourth man rose to speak.
(3)由几个序数词和基数词在拼写时不对应,很容易写错,应特别注意。它们是:one---first, two---second, three---third, five---fifth, eight---eighth, nine---ninth, twelve---twelfth 。
(4)表示年,月,日时, 年用基数词表示,日用序数词表示。例如:
1949 年十月一 日 读作 : October (the) first, nineteen sixty
2004 年九月十 日 读作: September (the) tenth, two thousand and four
(5)表示分数时,分子用基数词表示,分母用序数词表示。分子大于 1 时,分母加 -s 。例如:
three fourths, one second, wo fifths
(6)序数词有时用缩写形式:
first → 1st, second → 2nd, third → 3rd, fourth → 4th, twenty-second → 22nd
英语中的数词是指表示数目多少或顺序先后的词。表示数目多少的数词叫基数词，如 one, five, ten, thirty,sixty-five 等；表示顺序先后的数词叫序数词，如 first, sixth, tenth, twenty-first 等。数词用法相当于名词和形容词，在句中可用作主语、宾语、表语、定语、同位语等。
参考资料
百度知道：https://wenku.baidu.com/view/ee39ae04f011f18583d049649b6648d7c1c708e5.html
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1. 表示确切数目时，hundred，thousand 和 million 只能用单数，不能用复数；但表示不确定的数目时，要用复数并加of
例：three hundred 三百 eight thousand 八千
hundreds of 成百上千的 thousands of 成千上万的
millions of 数百万的
2. 基数词可以用来表示年龄
例：He is ten years old. 他十岁了。
in his twenties 在他二十几岁时
3. 基数词可以用来表示时间
例：6:30 six thirty / half past six
7:45 seven forty-five/a quarter to seven
9:00 nine o’clock
4. 基数词可以用来表示年代
例：1990年读作nineteen ninety
2005读two thousand and five
5. 基数词可以表示某事物的编号
例：第三部分 Section 3
606房间 Room 606
电话号码 4303639 TEL 4303639
6. 基数词可以用于某些数学算式
例：2+1=3 Two and one is three.
8-6=2 Eight minus six is two.