Comments by "cosmosofinfinity" (@cosmosofinfinity) on "Numberphile"
channel.
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How about, let's say you choose the left door, and he reveals a zonk in either the remaining middle door or right door. 2 in 3 times your original choice landed on the zonk, odds are against you. But when he shows you a door with a zonk (be it the middle door or the right door he chooses to reveal), only 1 in 3 times are they BOTH zonks.
Which means 2 out of 3 times, only one of the two doors he can choose to psyche you out with had a zonk to do that with, and he just showed it, leaving the last remaining door zonk-less, and he showed the only zonk he could show (the only one he NEEDED to show). With only three possible arrangements of these doors, and the left door being your initial choice as the constant:
Sequence 1: ☐ | ☒ ☒
Sequence 2: ☒ | ☐ ☒
Sequence 3: ☒ | ☒ ☐
As you can see, 2 of these 3 sequences has the selectively unrevealed door to be zonk-less. Them both being rigged with zonks after he chose to reveal one is just 1 out of those 3 arrangements. Still absolutely a real possibility, but it is only 1 of the 3 possible sequences. Your two-thirds zonks risk became one-thirds zonks risk after one has been confirmed eliminated.
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