This is the first time I’ve been to China.
The 20th century has seen the bloodiest wars in the history of humankind.
Jill is the most intelligent girl in the class.

a/one hundred, a/one thousand, a/one million
one and a half kilos (or a kilo and a half)
a/one third
a/one quarter

But:

two thirds

Also:

quarter of an hour
half a minute