>>11337088No, the possible combinations that are left are GB, BG, and GG. So the probability is 2/3.
If you flip a coin twice, you have 4 possibilities: HH, TH, HT, TT. (H = heads, T = tails)
You're assuming that TH and HT are the same, so that you only have HH, TH, and TT.
Then you say that if you discount all HH, there's a 50% chance it's TH.
Go try that out in practice and see how that theory works out for you.