Since there are 52 cards in a deck (It's a miracle they didn't lose any- I always lose cards), and half of those are red, 26 cards are red (with the other 26 being black), and since there are four of each number card in a deck, there would be four threes. So the probability that you choose a red card would be 1/2 (50%, if you need percentages), while the probability that you choose a card with a three would be 4/52, or 1/13 (7.7%).
