Re: Probabilty Riddles
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For question 1.
You either picked the right door off the bat or you didn't
Probablity that you picked the right door is 1/3 so the chances that door B is correct is 1/3. Conversly the probability that you picked the wrong door is 2/3 so the chances that the other door is correct is 2/3.
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Huh? The new information tells you that your choice has 50% chance of being correct so switching does you no good. The answer quoted (switch doors) must be a silly play on words.
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No, switching doors is indeed correct. I know I'm just restating the above, but think of it this way. If you pick the wrong door, the host shows you the other wrong door. You then switch and get the correct door. What is the probability of picking the wrong door originally? 2/3. Now if you pick the right door originally, the host shows you randomly one of the two wrong doors, and then you unfortunately switch to the other wrong one. What is the probability of picking the right door originally? 1/3. So it is indeed correct to switch and you will win with 2/3 probability.
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