Learn Italian: Abbiamo cinquanta euro.

Italian verbs change depending on who is doing the action. The verb abbiamo comes from avere (to have) and specifically means "we have." Because the verb itself tells us who the subject is, you don't need to add the pronoun noi (we) unless you want to emphasize it.

How do I know whether to change the ending of cinquanta to match a plural noun?

You don't have to! In Italian, cardinal numbers like cinquanta (fifty) are invariable, meaning their endings never change to match the gender or number of the noun they describe. The only exception to this rule is the number one (uno).

If I wanted to say "fifty-one" or "fifty-eight", does cinquanta stay exactly the same?

Not quite! When you combine a "tens" number like cinquanta with a number that starts with a vowel, like uno (one) or otto (eight), you drop the final "a". So, fifty-one becomes cinquantuno and fifty-eight becomes cinquantotto. For other numbers, you just combine them normally without dropping any letters: cinquantadue (fifty-two).

Wait, there are fifty of them. Why doesn't euro end in an "i" like a normal masculine plural noun?