Ranked Leagues

I have a question. How do the ranked leagues work. I mean, I got placed in Singed Ravens Silver V today. My duo queue friend just got promoted a couple of minutes ago.. to Singed Ravens. My second account (which I placed first) got into... Singed Ravens. And my support buddy also promoted a couple of weeks ago to Singed Ravens. Pure luck? Geographically? Friend based? Only one Silver V? It feels weird.
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