It varies depending on your opponents. Assuming no previous ranked play, you could hit a hot streak and find yourself in Silver or Gold. Then again, you could start off with a winstreak be playing with golds and silvers for the first game or two (looking at Gold) - and then you hit a cold patch. Suddenly you lose one due to an afk, then another due to trolls and an afk, and another which has the guy who rages and ints - and suddenly you are looking at bronze.
A perfect record for a brand new account (no previous ranked play on it) can get low Gold or high Silver. But never discount the effects of randomness. One person in my friend list went 50% winrate and got Silver 5 yet another managed to somehow win 30% of his placement games and got the same tier.