the term 'skill group' is a little misleading, simple way to explain it as you really dont know how there formula works is that you have an MMR (you cannot see this magical number). The 'skill groups' ie gold 1 would be assigned to people whose MMR is in a certain range. You will lose or gain MMR when you lose or win a match, if your MMR drops out of the gold 1 range and into the silver master elite range you would derank to that 'skill group'. Competitive will use players MMR to match people together so you could have a range of ranks in one game as it will work on the average MMR of the team. So in your question there is no way for someone to tell you that it all depends on how much MMR you lose per game and what your MMR was to start with. The reason i say the term skill group is misleading is because to much emphasis is placed on it, by that i mean you could be gold 1 and be playing against a gold 2, but there could be so little difference in your MMR that it makes no difference other than the little rank picture that is put against your name.