知识要点
表示“多少”和“第几”的词，叫数词。数词分为基数词和序数词两种。
1)基数词：在十位数词和个位数词中间加上连字符 “ - “ 。如： 21 twenty -one‘基数词三位以上的数词， 在百位和十位之间，一般要用连词"and “。 如： 132 one hundred and thirty-two.
表示”万“的词英语中没有。如1万可用10千来表示。 ten thousand. 30万可用 three hundred thousand 来表示。
基数词的用法：
1.编号的事物用基数词： 如：Lesson Five， Room 101
2.表示”年，月，日“ 时用基数词。
3.表示 “几点钟， 几点过几分” 用基数词。It is two to two. 现在是两点差两分。
4.加减乘除用基数词。 One plus two is three.一加二等于三。Eight minus four is four. 八减四等于四。
Two times two is four.二乘二等于四.Ten divided by two is five.十除二等于五。
5表示百分数用基数词.
Thirty percent of them is water. 它们当中有30%的水。
6.表示分数时，分子数字用基数词， 但分母要用序数词， 如分子不是1，序数词要用复数形式。
One-fifth of the books are mine. 三分之一的书是我的。
Three-tenths of water is disappeared. 十分之三的水不见了。
2)序数词：表示数目顺序的词用序数词。
1.序数词1━19 除第一，第二，第三，第五，第八，第九， 第十二变化不规则外， 其余均由在基数词后加上 -th。
2.十位整数的序数词的构成方法是， 是将十位整数基数词的词尾 -y 变成 i 再加 -eth。
3.几十几的序数词，只是把个位数变成序数词， 十位数不变。
4.第一百以上的多位序数词 由基数词的形式变结尾部分为序数词形式来表示。
one hundred and twenty-first ，one thousand，three hundred and twentieth
5.序数词的缩写形式 有时，序数词可以用缩写形式来表示。主要缩写形式有。
first--lst second--2nd third--3rd fourth--4th sixth--6th twentieth--20th twenty-third--23rd 其中lst，2nd，3rd为特殊形式，其它的都是阿拉伯数字后加上th。
6.通常前面要加定冠词 the；但是如果序数词前出现不定冠词a或an时，则表示“再”，“又”.
We’ve tried it three times．Must we try it a fourth time？
7.基数词也可以表示顺序。只需将基数词放在它所修饰的名词之后(名词需大写) 即可，不需要添加定冠词。
the first lesson-Lesson One ，the fifth page-Page 5， the twenty-first room-Room 21
练习
)1. I‘ve read ______ sports news about the F1 race today.
A. two B. pieces C. two pieces D. two pieces of
)2. During World War II， a Jewish（犹太）lady was protected by a local family in Shanghai in her ______.
A. fifties B. fifty C. fiftieth D. the fiftieth
)3. The river through our city， which is about _________， is clean again.
A. 6000 meters long B. 6000-metres-long
C. 6000-metre-long D. 6000 meter long
)4. I study in Yu Cai Middle School. There are two ____students in our school.
A. thousand B. thousands C. thousand of D. thousands of
)5. They said they would have holiday.
A. a two-month B. two months C. two-months D. two-month’s
) 6.-When was the PLA founded？
-It was founded on ____.
A. July 1. 1921 B. October 1.1949
C. May 1.1922 D. August 1.1927
) 7. In the past two years， many tall buildings have been built in our city. The tallest is an that stands in the centre.
A. 80-floor building B. 60-floor building
C. 80-floor buildings D. 70 floors building
)8.The number of people invited ____ fifty， but a number of them _____absent for different reasons.
A. were ； was B. was ； was C. was ； were D. were ； were
)9.- How soon will you finish your work？ -In about _______.
A. one and a half month B. one month and a half
C. one and half a month D. a month and half
)10.-Would you like some fruit， madam？ -Oh， yes. _______， please.
A. 5 kilo bananas B. 5 kilos of bananas
C. 5 kilo of bananas D. 5 kilos of banana