1. Tenis a simple cardinal noun.
2. Secondis a simple ordinal noun. In most cases nouns premodified
by ordinals take the definite article. In these cases they
show the order of persons or things in a series.
3. 4. Twenty, eighteenand sevenare cardinal numerals.
Sevenis simple and the other two are derivatives, formed by the
means of the suffixes -teen and -ty.
5-8. The twoand a four, tensand hundredsare substantivised
numerals.
9. Twois a simple cardinal numeral and millionsis a substantivised
numeral. Of is indispensable in this case precisely
because millionsis substantivised.
10. This is a composite cardinal numeral. In most cases the
words dozen, hundred, thousand, millionand billiontake
no -s after other cardinal numerals because they are not substantivised.
11. See 10.
12. See 9.
13. This is an ordinal numeral. The noun it premodifies is
used with the indefinite article because ordinal numerals maybe
used with the indefinite article when they do not show a definite
order of persons or things in a series, and this is just the case:
a thirdhere means merely anotherand loses its numerical
meaning.
14. See 13.
15. This is a fractional numeral.
16. Since Man is supposed to have just five universally recognized
senses, a sixth one does not belong to a definine, scientifically
recognized number. So it quite safe to say “a sixth sense”,
meaning another, an additional one. In other words sixthlooses
its numerical meaning.
17. A first nightis a set phrase meaning the evening when
the first public performance of a show, play etc. is given. It usually
takes the definite article but one may say a first night performance
or a first night partybecause here first nightis
used attributively and the indefinite article refers to the nouns
premodified by them.
18-19 A first timeand a first lovejust like other firsts like,
say, a first love-makingare used with the indefinite article if
there is no limiting attribute and no limitation is clear from the
context. By the way «ëþáîâü ñ ïåðâîãî âçãëÿäà» is “love at
first sight”.It happens so quickly that everybody forgets about
articles.
20. Secondis an ordinal numeral. It is preceded by the indefinite
article which refers to the noun computer.