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今天和大家分享数词中的序数词、分数、小数、和百分数等方面的知识点。
英语词法 之 序数词与分数、小数和百分数
一、序数词
数词分为基数词和序数词两种。我已经在上一章总结了基数词和不定量数词的用法，现在来说说序数词。序数词表示顺序，一般由与之相应的基数词词尾加词尾-th构成，但要注意特殊形式。
1．常用序数词列表：
Ⅰ | Ⅱ | Ⅲ |
1 first 2 second 3 third 4 fourth 5 fifth 6 sixth 7 seventh 8 eighth 9 ninth 10 tenth | 11 eleventh 12 twelfth 13 thirteenth 14 fourteenth 15 fifteenth 16 sixteenth 17 seventeenth 18 eighteenth 19 nineteenth | 20 twentieth 30 thirtieth 40 fortieth 50 fiftieth 60 sixtieth 70 seventieth 80 eightieth 90 ninetieth 100 hundredth |
附：基数词变序数词歌诀：
基变序，很容易，结尾加上-th；
一二三特殊记，结尾分别是t, d, d；
八去t， 九去e，f 来把ve替，y改为“ie”，结尾仍有-th；
若是遇到几十几，只变个位就可以。
2.序数词注意事项：
(1)序数词前一般要加限定词the 或代词。
例如：I have already got two letters from Susan this year. So this is the third one.
This is her second visit to Japan, isn't it?
(2)一百以上的序数词的变化是在基数词的基础上，个位数变成序数词。
例如：Three hundred and two → three hundred and second
two hundred and twenty-one → two hundred and twenty-first
(3)序数词前有时可用不定冠词a，表示“另一个、再一个”。
例如：Just at that moment a second bullet came by, then a third, a fourth, ….
The women who had been invited got to the hall, let’s show them a third table.
We have got five players in our groups. We need a sixth one.
3.序数词的其他用法
(1)表示编号
编号既可以用基数词，也可以用序数词，但表达形式不同。
例如：Part one = the first part
Lesson Three = the third lesson
World War II(Two) = the Second World War
(2)世纪、日期的表达法
e.g.The Romans conquered Britain in the 11th century.
May 4th (4)
August 1st, 1927
二、分数、小数和百分数的表示法
1.分数
分数的表达法是分子用基数词，分母用序数词，分子大于1时分母用复数形式。
在表示二分之一时，分母常用half, 表示四分之一的时候，分母可以用fourth 或者quarter。例如：
1/2 a / one half
1/3 a/one third 2/3 two / thirds
1/4 a / one forth 或a / one quarter 3/4 three fourths 或 three quarters
1/5 a /one fifth 2/5 two fifths
1/6 a / one sixth 5/6 five sixths
2. 小数
小数的表示方式和汉语中小数的表示方式基本一样，小数点后的数字是“见几读几”，点用point表示。例如：
e.g.27.832 twenty-seven point eight three two
0.125 zero / o point one two five
3. 百分数
百分数的表达方式比较简单，在基数词或者小数的后面加上percent就可以。例如：
40% forty percent
0.3% (zero) point three percent
4. 倍数表示法
(1)… times as … as …
例如：The output of cars in 1994 was six times as many as that of 1987.
(2)… times that of …
例如：The output of cars in 1994 was six times that of 1987.
(3)… times 名词 of…
例如：This iron is three times the size of that one.
(4)… times that of … 与… times what –clause
例如：The output of cars in 1994 was five times greater than that of 1987.
The output of cars in 1994 was six times what it was in 1987.
5. 作状语作序数词，这时序数词前的冠词通常省去。如序数词前出现形容词性物主代词或名词所有格，这时序数词前的冠词也省去。
例如：The Yellow River is China's second longest river.
What shall we do first?
The Changjiang River is the fourth longest river in the world.
9．数词前可加every，表示“每一段时间或每一段。。。”
例如：every four days = every fourth day 每四天
作者介绍：
仓颉Sophy，英语爱好者，爱好文学和旅游，敬请【关注】我，我将持续更新和分享我在英语方面的见解。
