The ranked system

So basically i was playing my promos and i went 4 and 6 and got bronze 1 (was silver 3). I wasnt to mad about this considering i didnt do to well but the thing that really pissed me off was that my often duoing partner (was silver 3 also) went 3 and 7. Im making fun of him because he should get like bronze 2 right? No the fucker gets silver this makes no sense to me and just seems dumb. can someone please explain why this shit is still happening in league? its really tilting me