(1) 基数(Cardinal numerals)：one, two, three...

(A) 除one接单数名词外，其余均接复数名词。
He has one sister and three brothers.

(B) hundred的后面须加and（但可以省略）。
12,345 = twelve thousand three hundred (and) forty five;

(2) 序数(Ordinal mumerals)：first, second, third...

(A) 序数前面必须附以定冠词。而a second, a third等，则是another的意思。

(B) 日期多用序数。
It’s on Friday, the fifth of October (= October the fifth = October 15th).

(C) 序数的简体。
9th = the ninth; 12th = the twelfth; 16th = the sixteenth;

(3) 分数：

(A) 分数的表示法：第一，分子用基数，分母用序数。第二，分子大于2时，分母须加“s”以形成复数。
1/2 = a (one) half; 1/3 = a (one) third; 2/3 = two-thirds; 1/4 = a (one) quarter;

(B) 分数可接与不可数名词；所接的名词是单数，则与单数动词连用，是复数则与复数动词连用。
A third of the peach was bad.
A third of the bananas were bad.

(4) 倍数词：常用的有half, double, treble（三倍）等。

(A) half a, a half, half the ＋名词，表（一半的）。
He ran a half mile in half an hour.
He ran half a mile in half an hour.
I have read half the book.

(B) half还可作名词，代名词及副词。
Two halves make a whole. （名词）
This is half as much again as that. （副词）

(C) 倍数常用的表达法：
(half; double; treble; twice; two times; three times; four times...) ＋定冠词或所有形容词＋名词或所有代名词
I had to pay double (= twice) the usual fare.
That window is three times the size of this.