I had a deck of cards but I lost a few. When I play with 3 other people, I have 3 cards left. When I play with 2 other people 2 cards are left. When I play with 4 other people, I have 2 cards left. how many cards have I lost?

You have lost 5 cards.

In a normal deck of cards, there are 52 cards. If you take those 5 cards away, you have 47 cards.

If you are playing with 3 other people (meaning 4 people total), each person gets 11 cards (totaling 44 cards) and leaving 3 cards left over.

If you are playing with 2 other people (3 people total), each person gets 15 cards (totaling 45 cards) and leaving 2 cards left over.

If you are playing with 4 other people (5 people total), each person gets 9 cards (totaling 45 cards) and leaving 2 cards left over.

Thus meaning, you have lost 5 cards. I hope this helps!