知識要點
表示多少和第幾的詞，叫數詞。數詞分爲基數詞和序數詞兩種。
1)基數詞：在十位數詞和個位數詞中間加上連字符 - 。如： 21 twenty -one‘基數詞三位以上的數詞， 在百位和十位之間，一般要用連詞"and 。 如： 132 one hundred and thirty-two.
表示萬的詞英語中沒有。如1萬可用10千來表示。 ten thousand. 30萬可用 three hundred thousand 來表示。
基數詞的.用法：
1.編號的事物用基數詞： 如：Lesson Five， Room 101
2.表示年，月，日 時用基數詞。
3.表示 幾點鐘， 幾點過幾分 用基數詞。It is two to two. 現在是兩點差兩分。
4.加減乘除用基數詞。 One plus two is three.一加二等於三。Eight minus four is four. 八減四等於四。
Two times two is four.二乘二等於四 divided by two is five.十除二等於五。
5表示百分數用基數詞.
Thirty percent of them is water. 它們當中有30%的水。
6.表示分數時，分子數字用基數詞， 但分母要用序數詞， 如分子不是1，序數詞要用複數形式。
One-fifth of the books are mine. 三分之一的書是我的。
Three-tenths of water is disappeared. 十分之三的水不見了。
2)序數詞：表示數目順序的詞用序數詞。
1.序數詞1━19 除第一，第二，第三，第五，第八，第九， 第十二變化不規則外， 其餘均由在基數詞後加上 -th。
2.十位整數的序數詞的構成方法是， 是將十位整數基數詞的詞尾 -y 變成 i 再加 -eth。
3.幾十幾的序數詞，只是把個位數變成序數詞， 十位數不變。
4.第一百以上的多位序數詞 由基數詞的形式變結尾部分爲序數詞形式來表示。
one hundred and twenty-first ，one thousand，three hundred and twentieth
5.序數詞的縮寫形式 有時，序數詞可以用縮寫形式來表示。主要縮寫形式有。
first--lst second--2nd third--3rd fourth--4th sixth--6th twentieth--20th twenty-third--23rd 其中lst，2nd，3rd爲特殊形式，其它的都是阿拉伯數字後加上th。
6.通常前面要加定冠詞 the；但是如果序數詞前出現不定冠詞a或an時，則表示再，又.
We’ve tried it three times．Must we try it a fourth time？
7.基數詞也可以表示順序。只需將基數詞放在它所修飾的名詞之後(名詞需大寫) 即可，不需要添加定冠詞。
the first lesson-Lesson One ，the fifth page-Page 5， the twenty-first room-Room 21
練習
( )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（猶太）lady was protected by a local family in Shanghai in her ______.
A. fiftiesB. fiftyC. fiftiethD. 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-monthB. 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
( ) 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
