Its possible that to them, the scores aren't important and its a more conducive (and realistic) learning environment if they work together to solve the problems rather than doing it alone. There are many advantages:
* rather than just giving up on a problem, you can talk it out and learn together
* you get the opportunity to teach the material that you think you know that others find hard (a good heuristic for problems you may have just barely understood, but gotten correct anyway). Teaching material is a great way to learn it, and expose any gaps you might have in your knowledge.
* instant feedback on problems while they are still fresh in your memory