Is the twenty first of October, el veintiún de octubre, or el veintiuno de octubre?
I want to know the correct way to write the twenty first of a month when doing dates. Is it "el veintiún de mayo" or is it "el veintiuno de mayo" ?
3 Respuestas
apocopation deals with adjectives, not nouns.
Uno becomes un before a masculine, singular noun. (as does veintiuno)
So are days of the month adjectives or nouns?
Is it the el dieciocho [día] de Octubre, just like with time it is "son las tres [horas]"? o son las [horas] tres.
To get your answer lookup whether it is el primer [día] or el primero de Octubre.
el día primero. el día veintiuno
I actually learned it both ways but I have seen more of your first answer as of late. If you look up in the flashcard section there is a great set in regards to this. I am getting ready to have students come in so I can't actually look. Hope this helps!! 
I believe that it would be "el veintiuno de mayo" because numbers ending in "-uno" only change to "-ún" or "-una" endings when they are modifying masculine or feminine nouns, respectively.
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