157. Nouns may be formed from the cardinals by addition of the ending
"-o." After such nouns the preposition "da" or "de" is used:
dekduo = a dozen. milo = a thousand.
dudeko = a score. unuo = a unit.
deko = a ten, half a score. kvaro = a four, a quartette.
cento = a hundred. trio = a three, a trio.
[Footnote: The prepositions "da" and "de" follow nouns (99, 100) or
adverbs (101), while "el" follows adjectives in the superlative degree
(75), cardinal numerals (138), and the pronouns tiu, kiu (106), etc.:
"dekduo da ovoj", a dozen (of) eggs. "dekduo de la ovoj", a dozen of the
eggs. "dek du el tiuj ovoj", twelve of those eggs. "kiu el la ovoj?"
which one of the eggs? "tiu el la ovoj", that one of the eggs. "la plej
fresxa el la ovoj", the freshest of the eggs.]
158. Adverbs may be formed from the cardinals by addition of the ending
"-e":
unue = firstly, at first. deke = tenthly.
due = secondly, in the second place. sesdeke = sixtiethly.
kvine = fifthly, in the fifth place. okdek-kvare = eighty-fourthly.