Could I get A Rioteer to answer a question?

Quick foreword this isn't a rant, and it isn't me crying about how broken the ranked system is. I have every intention of digging myself out of the shit hole that is Bronze. Now, the question is pretty concise; my friend won 4/10 of his placements, and got placed Silver 5; I won 8/10 of my placements, and got placed Bronze 5. How? Now I'm sure there's some math or logical reason this happened, but I would really like to know it, because this is frustrating, and it doesn't seem very fair. (To be clear I did well all 10 games it wasn't like I got hard carried through my placements, and I did them solo.) So thank you in advance for answering my query if you do. In the mean time I'll be grinding away at that soloQ ladder desperately trying to save myself from Bronze. Peace! [slayer-jinx-catface]