序数词在句中可用作下列各个句子成分：

1)主语

The first is better than the second.第一个比第二个要好。

2)宾语

He was among the first to arrive.他是首批到达的。

3)定语

China exploded its first atom bomb in October 1964.中国于1964年10月爆炸了第一颗原子弹。

His father died in the Second World War.他父亲在第二次世界大战中死去。

4)表语

Jack is always the first to get to the office in the morning.杰克每天早晨总是第一个到办公室。

[注]序数词前面常用定冠词the。

分数和小数的读法

1)分数(fraction)分子为基数词，分母为序数词并有复数。

1／2 one half [hB:f]； 1／3 one-third； 2／3 two-thirds；

1／4 one-fourth或 one quarter [5kwC:tE]； 3／4 three-fourths或 three quarters； 2 3/5 two and three-fifths.

2)小数(decimal)

0.5 zero [5ziErEu] point five； 1.25 one point two five； 3.458 three point four five eight.