How is the teams in ranked determined?

My past few ranked matches have been nightmares. I have had a Pantheon support and a Ziggs support which were totally useless. Why is it that I can not be matched against them but rather, lose LP, get demoted and get upset because they are on my team? So my question is how does rito determine which player is on which ranked team? Cause the incompetence or lack of understanding the game on my teams is driving me insane. SO does anyone have any ideas?