I may be wrong about this, actually. Guess that goes to show you that precise terminology matters here. This python gist appears to simulate the situation corr

I may be wrong about this, actually. Guess that goes to show you that precise terminology matters here. This python gist appears to simulate the situation correctly, and shows that it becomes 50/50. https://gist.github.com/ecdavis/da8f67258860e9f35620 https://gist.github.com/ecdavis/da8f67258860e9f35620 That said, I'm not sure I completely agree with this solution just throwing out cases where he opens the winning door, without replacement. I feel like at this point we're calculating a different problem where we haven't precisely defined what it is we're measuring, so you could tweak things to get either answer.