How does ranked matchmaking work?

So my friend has been solo-q-ing for about 6 games. He's won 5 of 6. I checked his teams and they all seemed fine, okay whats the problem? What about other players? I've played 4, winning 1 because EACH and EVERY game, i get a feeding team or maybe 1 decent player. How is this happening? How are some players getting actual, communicating (yes, the teams i've come across have genuinely not said a word throughout the entire game), decent teams? I'm only creating this thread because it's an enormous difference in team balance between my friend and I. I try my best to tell the non-cooperative players that we need dragon, group etc. but nothing ever seems to work and it's simply impossible to climb at all but my friend has a breeze with these know it all teams that he so luckily finds? Is there logic behind this or just an absolutely ridiculous coincidence?
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