Can I mix my Magic: The Gathering decks?

Hey, I'm really new to Magic and this may be a really stupid question but: I've just been given a Knights vs Dragons set (I took Dragons) and a New Phyrexia, Feast of Flesh set. I just wanna know if I can mix the two as long as I keep it 60 cards+ and no more than 4 single cards (other than lands). Thanks!