The names of certain quantities are formed from the cardinal numbers
by adding "o", as "dekduo", a dozen; "dudeko", a score; "cento", a
hundred; "milo", a thousand. These names, as well as names of quantities
generally, require to be followed by "da", of, as "dekduo da birdoj", a
dozen (of) birds, but "dekdu birdoj", twelve birds; "dudeko da pomoj", a
score of apples; "cento da sxafoj", or "cent sxafoj", a hundred sheep;
"milo da homoj", a thousand people; "miloj da homoj", thousands of
people.
When these expressions form the object of the verb, it is the name of
the number which takes "-n", not the noun which follows "da", as "Li
acxetis dudekon da sxafoj", He bought a score of sheep.
For "firstly, secondly", etc., "-e" is added to the number, as "unue",
firstly; "kvine", fifthly; "deke", tenthly. (See Lesson 12).