Los números: cinco reglas

Five rules (cinco reglas) to remember (para recordar) about numbers in Spanish:

1.From 16 to 29, the numbers are written in one word: it is not "diez y seis" but "dieciséis"; "veinte y dos" but "veintidós" and so on.

2. We use "Y" (and) only between tens and unities ("treinta y ocho", "cuarenta y siete", etc), not after hundreds and thousands: it is not "doscientos y treinta y cuatro" but "doscientos treinta y cuatro"; "tres mil y quinientos" but "tres mil quinientos" and so on.

3. "Uno", "un" or "una"? When number one is followed by a noun, it loses the letter -O: "Tengo un perro" (I have a dog). Why? Because the number has turned into the indefinite article. Thus if the word is feminine, "uno" will become "una": "Tengo una bici" (I have a bike). The same happens with "cientos": "Tengo quinientos euros" (I have 500 euros), but "Tengo quinientas rupias" (I have 500 rupees).

4. Comma or dot? In Spanish the punctuation of numbers works in the opposite way than English punctuation: the dot is used to separate thousands.

5. "Un billón" = one million millions, not one thousand millions!