(1) 基数词在句中主要用作主语、宾语、定语、表语、同位语，例如： Thirty of them are Party members.(主语) --- How many would you like? --- Three ，please.(作宾语) The nine boys are from Tianjing.(定语) Six plus four is ten.(表语) We four will go with you.(同位语) (2) 表示一个具体数字时，hundred, thousand, million一律不用复数;在表示一个不确定数字时则用复数。例如： Our country has a population of 1,300 million people. There are three thousand students in our school. After the war, thousands of people became homeless. Maize is the most important food crop for millions of people in the world. They arrived in twos and threes. (3) 表示“……十”的数词的复数形式可用来表示人的岁数或年代，例如： He is in his early thirties. He died still in his forties. This took place in 1930s. (4) 表示时刻用基数词。例如： We get up at six. The workers begin work at eight. 表示“几点过几分”，用介词past,但须在半小时以内。例如： ten past ten, a quarter past nine, half past twelve 表示“几点差几分”用介词to, 但分数须在半小时以上。例如： twenty to nine, five to eight, a quarter to ten 表示“几点几分”还可直接用基数词。例如： seven fifteen, eleven thirty, nine twenty
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. 注意事项： 三位数数词要在百位和十位(若无十位则和个位)之间加and。 1，000以上的数字，从后向前第三位数加一个“，”，第一个“，”前为thousand，第二个“，”前为million，第三个“，”前为billion。 2.序数词除了first，second，third外，其余都在基数词尾加-th构成。 3.分数分子在前，分母在后，分子用基数词，分母用序数词，当分子大于1小时，分母序数词要变成复数。 4.Hundreds(thousands，millions)of……用法。