定义：表示数目多少或顺序多少的词叫数词，数词分为基数词和序数词。表示数目多少的数词叫基数词;表示顺序的数词叫序数词。
I基数词
1.基数词的构成
(1)1-20
one,two,three,four,five,six,seven,eight,nine,ten,eleven,twelve,thirteen,fourteen,fifteen, sixteen, seventeen, eighteen, nineteen, twenty
(2)21-99 先说“几十”，再说“几”，中间加连字符。
23→twenty-three,34→thirty-four,45→forty—five,56→fifty-six,67→sixty-seven,78→seventy-eight,89→eighty-nine,91→ninety-one
(3)101—999先说“几百”，再加and,再加末两位数或末位数;
586→five hundred and eighty-six,803→eight hundred and three
(4)l,000以上,先从右往左数，每三位数加一个“,”,第一个“,”前为thousand.第二个“,”前为
million,第三个“,”前为billion(美式)或thousand ,million(英式),然后一节一节地表示。
1,001→one thousand and one
9,785→nine thousand, seven hundred and eighty-five
18,423→eighteen thousand, four hundred and twenty-three
6,260,309→six million two hundred and sixty thousand three hundred and nine
750,000,000,000→seven hundred and fifty, billion(美式) seven hundred and fifty thousand million(英式)
2.基数词的用法
(1)作主语
eg.Four Of them come from Paris.
(2)作宾语
eg.一 How many books would you like?
一I would like two.
(3)作表语
eg.Seven minus two is five.
(4)作定语
eg.There are three people in my family•
(5)作同位语
eg. You two will go swimming with us.
(6)表具体数字时,hundred, thousand ,million用单数。
eg. There are six hundred students in our grade.
(7)表不确定的数字时,数词用复数。若带名词，再加of。 hundreds of(数百,成百上千的),thousands of(数干,成千上万的),millions of(数百万)two thousand (两千)
Thousands and thousands of people have visited the city.成千上万的人参观了这座城市。
(8)在一些表示“一排”或“一组”的词组里;
eg,They arrived in two sand threes.他们三三两两地来了。
(9)表示“…十”的数词的复数可以表示人的岁数或年代。
eg. He is in his early thirties.他有三十来岁(31—34岁)：
This took place in the 1930s.这事发生在二十世纪三十年代;
(10)表示时刻
钟点表达法。
顺读法(钟点+分钟) 如：4:30 four thirty 4:45 four forty-five 4:15 four fifteen 倒读法(分钟+to/past+钟点)
如：4:30 half past four
4:15 fifteen past four/a quarter past four 4:45 fifteen to five/a quarter to five
eg.I watch CCTV News at seven o’clock every evening.
(11)表示百分数
百分数的表达方式是：基数词+ percent(单数形式)+of+名词。如：
Thirty percent of the students in my class are from cities. 我班30%的学生来自城市。
About 61 percent of the surface is covered by water. 大约61%的表面被水覆盖着。
(12)小数的读法：小数点读作"point"，小数后各位数要分别读， 小数点前的数若为"0"可略去不读。
Examples： 2.468 读作：two point four six eight
0.157 读作：(zero)point one five seven
II 序数词
1.序数词的构成
(1)一般在基数词后加th
eg.four→fourth,thirteen→thirteenth
(2)不规则变化
one→first, two→second, three→third, five→fifth,eight→eighth,
nine→ninth,twelve——twelfth
(3)以y结尾的十位整数，变y为ie再加th
twenty→twentieth, forty→fortieth, ninety→ninetieth
(4)从二十一后的“几十几”直至“几百几十几”或“几千几百几十几”只将个位的基数词变为序数词。
twenty-first,two hundred and forty-fifth
2.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分数词的表达
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。
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