New ranked rank

Helo i wonder can someone tell me how the system calculate which rank will you be premoted in after you finish the first 10 ranked games i think that system neither need a rework or just i dont understand it. I mean a friend of mine who just registered and reach lvl 30 and get his first 16 champs started to play ranked he lost 8 of 10 of his games and he was promoted in Silver 4 and i have 1200+ games and after i win 5 of 10 games i was promoted in bronz 4 I dont know why and if someone explain me i would appreciate it.