The Cardinal Numbers may be used as nouns, by the addition of the ending -o. Thus, unuo, a unit; trio, a trio; dekduo, a dozen; dudeko, a score; cento, a hundred; milo, a thousand. Note that miliono is ALWAYS used as a noun.
When a number or any other word is used as a noun of quantity, the noun which follows it must be preceded by the quantitative preposition da:—Dekduo da ovoj, a dozen eggs; milo da soldatoj, a thousand soldiers (one might of course also say dek du ovoj, mil soldatoj); du metroj da drapo, two metres of cloth; tri funtoj da sukero, three pounds of sugar.
Ordinal Numbers.
The Ordinal Numbers are formed by adding the adjectival ending -a to the Cardinals. In Compound Ordinal Numbers, the groups of hundreds, tens, units, etc., are joined by hyphens, and the ending -a is added to the unit numeral. Thus: unu, one—unua, first; tria, third; dek-unua, eleventh; tridek-sepa, thirty-seventh; kvarcent-sesdek-dua, 462nd, and so on. Written in figures these would be 1a, 3a, 11a, 37a, 462a. The Ordinals are of course inflected like adjectives. (See page [77].)
Fractions
Fractionals are formed by adding the suffix -on (plus the endings o, a, or e as required) to the Cardinal Numbers. Thus: unu duono, one-half; tri kvaronoj, three-quarters; dek sep dek-naŭonoj, 17/19; dudek tri kvarmil-kvincent-tridek-naŭonoj, 23/4539. Duone vera (or duonvera), half-true. Tri-kvaronoj da funto (or trikvaronfuntoj), ¾ lb. Duono da funto (or duonfunto), ½ lb.
Multiples, Collectives, and Distributives.
Multiple Numbers are formed from the Cardinals by adding the suffix -obl, with the requisite grammatical ending o, a, or e. Thus: duobla, double; duoblo, a double; duoble, doubly; tridekoble, thirty-fold; sesoble naŭ estas (or faras) kvindek kvar, six nines are fifty-four; duoble du estas kvar, twice two are four.
Collective Numerals are formed by the addition of the suffix -op (plus the grammatical termination required). Thus: duope, two at a time, two together; naŭope, nine at a time; ili venadis dekope, they came in tens; dumilopa taĉmento, a detachment two thousand strong.
Distributives are shown by the preposition po, meaning at the rate of. Thus: li aĉetis por ĉiu infano po ses pomoj, he bought six apples for each child; li ricevas po dek ŝilingoj por ĉiu tago, he gets ten shillings a day; la vagonaro veturas po sesdek mejloj en ĉiu horo (or ĉiuhore), the train travels at (the rate of) sixty miles an hour, etc.