数词
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。
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。
0.157 读作：(zero)point one five seven
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