To start of, let me clarify what I "know" about "uno", "un", and "una":

  • Uno is used when the object is not mentioned.
  • Un is when the object is mentioned.
  • Una is the feminine form of "Un".

(Again, please correct me if I'm wrong.)

With that said, how would these phrases be translated in Spanish. More importantly if we have a phrase where the amount is a two digit number or higher- except eleven- ending with 1 (i.e. 21, 41, 101), would the word "uno" change in certain conditions?

Phrases in question:

  • "En julio hay treinta y un días." translates to ".... thirty-one days."
  • "Francisco tiene veinte y un años." translates to "... 21 years" (I especially have trouble convincing myself that this is the correct way even though I hear it as "....y uno años."
  • "Las frutas cuestan cincuenta y un centavos" translates to "....fifty-one cents" (Again, hard to believe, so please clarify).
  • 1
    The "diccionario panhispánico de dudas" (doubts dictionary) from the Spanish Royal Accademy (RAE) has normally all the rules with really useful examples: lema.rae.es/dpd/?key=uno
    – Sergio Tx
    Commented Aug 30, 2016 at 11:13

1 Answer 1


Your examples are correctly translated. There is a rule to use 'un' when it is used as an adjective compound from one or more words and that precedes masculine nouns.

Veintiún libros.
Treinta y un lápices. 

But not when used with feminine nouns.

Veintiuna sillas.

Nor with prepositions

Veintiuno por ciento.

You can see the explanation here: http://www.rae.es/consultas/veintiuna-personas-veintiuno-por-ciento


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