The rule is that you use the article “a” before words that start with a consonant sound and “an” before words that start with a vowel sound. Both the words European and University have a consonant sound at the beginning ("Yur" for European and "Yu" for University, so you need to use "a". I hope this helps. :)

Thank you Lou & Brain :)

This is actually really interesting, I've never considered this before. Agreeing with the comment above, European has a 'y' sound therefore it doesn't need an 'an' because the sound isn't a vowel. The same happens with one way, one has a 'w'. University is also 'y' sound at the beginning. MP is an 'em' sound. So it needs the an. Maybe try saying the word out loud if you're having difficulty, it might help.

It is because of the way the sound of the word is. EUR makes the sound YER which is not a vowel sound. I had never thought about this before as an American. "American" starts our with the sound A so it needs an.