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。一、基数词
1)基数词写法和读法： 345 three hundred and forty-five;
2)基数词一般是单数形式，但下列情况，常用复数：
a. 与of 短语连用，表示概数，不能与具体数目连 用，如scores of people 指许多人;
b. 在一些表示"一排"或"一组"的词组里;
如：They arrived in twos and threes. 他们三三两两的到达了。
c. 表示"几十岁";
d. 表示"年代"，用 in +the +数词复数;
e. 在乘法运算的一种表示法里，如：3 x 5 = 15 Three fives is (are) fifteen.
二、序数词
序数词的缩写形式： first---1st second---2nd thirty-first---31st三、 数词的用法
1)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。
2)分数表示法
构成：基数词代表分子，序数词代表分母。分子大于1时，分子的序数词用单数，分母序数词用复数：
1/3 one-third ; 3/37 three and three-sevenths.
1.The new underground line is reported to be approximately __________ in length. - 35,000 = thirty-five thousand - 3,500 = three thousand five hundred - 350,000 = three hundred and fifty thousand 题干若来自听力或阅读，常会听到 “thirty-five thousand meters”。 2.According to the survey, nearly __________ of the respondents believe that artificial intelligence will reshape the job market within two decades. - 分母为 2 时用 half，不用 “second”。 因此 “2/3” 正确形式是 two-thirds，选 B。3.The error rate of the new algorithm is only 0.25%, which is significantly lower than that of the previous version, __________%. D. twenty-five hundredths 0.25 读作zero point two five（英式也可见 nought point two five）。 - D 虽数值上等于 0.25，但在科技语境中更常用 “zero point two five”。 4.Many social changes took place in the United States during __________, including the civil rights movement and the rise of counterculture. 表示年代用 the + 年份复数：the 1960s = 20 世纪 60 年代。 - B 的撇号形式多用于所有格，如 “in the 1960’s style”，非标准年代表达。 5.The output of renewable energy this year has increased by __________ compared with last year, reaching 12 million kilowatt-hours. “增加了两倍” 在英语中常用 increase by twice或 increase twofold。 - C “by two times” 语法可接受，但学术写作中不如 “by twice” 地道。 - D “double” 多作动词，如 “has doubled”。 
10个月宝宝每天需要喝多少奶粉？
