I have seen this explained elsewhere, but looks to be an illusion to me.
here's my logic. 2 rooms next to each other (cannot see each other), each with three doors. Contestant A selects Door A. Contestant B selects Door B. Door C is opened for both players (bobby prie 1). Which one has the prize? 50/50 chance. nothing else. There is a saying, you shouldn't believe everything you hear/see in a movie or read in the papers.
There may be only one possible way to convince the doubters, and that's to long hand every possiblity!
Mr Stickfast plays the game, and never, ever swaps! Here is every single possible combination of events for him:
[table="width: 650"]
[tr]
[td]prize behind[/td]
[td]he chooses[/td]
[td]they reveal[/td]
[td]percentage[/td]
[td]result[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 1[/td]
[td]door 2 or 3[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 2[/td]
[td]door 3[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 3[/td]
[td]door 2[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 1[/td]
[td]door 3[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 2[/td]
[td]door 1 or 3[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 3[/td]
[td]door 1[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 1[/td]
[td]door 2[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 2[/td]
[td]door 1[/td]
[td]11.11%[/td]
[td]
lose[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 3[/td]
[td]door 1 or 2[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td][/td]
[td][/td]
[td][/td]
[td]
wins[/td]
[td]
33.33%[/td]
[/tr]
[tr]
[td][/td]
[td][/td]
[td][/td]
[td]
loses[/td]
[td]
66.66%[/td]
[/tr]
[/table]
Mr Smartplayer switches every single time. Here is every possible combination of events for him:
[table="width: 650"]
[tr]
[td]prize behind[/td]
[td]he chooses[/td]
[td]they reveal[/td]
[td]percentage[/td]
[td]result[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 1[/td]
[td]door 2 or 3[/td]
[td]11.11%[/td]
[td]
loses[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 2[/td]
[td]door 3[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 1[/td]
[td]door 3[/td]
[td]door 2[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 1[/td]
[td]door 3[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 2[/td]
[td]door 1 or 3[/td]
[td]11.11%[/td]
[td]
loses[/td]
[/tr]
[tr]
[td]door 2[/td]
[td]door 3[/td]
[td]door 1[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 1[/td]
[td]door 2[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 2[/td]
[td]door 1[/td]
[td]11.11%[/td]
[td]
win[/td]
[/tr]
[tr]
[td]door 3[/td]
[td]door 3[/td]
[td]door 1 or 2[/td]
[td]11.11%[/td]
[td]
loses[/td]
[/tr]
[tr]
[td][/td]
[td][/td]
[td][/td]
[td]
wins[/td]
[td]
66.66%[/td]
[/tr]
[tr]
[td][/td]
[td][/td]
[td][/td]
[td]
loses[/td]
[td]
33.33%[/td]
[/tr]
[/table]
Basically, everytime he switches, he reverses his original result. As his orignal result was 33.3% win/66.7% loss, he has reversed that to 66.7% win/33.3% loss.
Try a practical experiment. Get your brother, mate or anyone that likes a little punt, that doesn't believe the figures above. Get 3 matchboxes, or coffee cups, or what ever can hide some coins. Let him hide $0.30 under one of the three without you seeing which one. You will pick one without ever touching the matchboxes/coffeecups. You pay him $0.10 and get to keep what you pick. He follows the rules, and reveals one of the empty matchboxes/coffee cups after you pick, and allows you to swap if you want. For goodness sakes, swap! Trust me, you'll win 2 out of 3 times. For every 3 times you do this, on average, you'll pay $0.30, and get $0.60 back. If he doesn't believe the figures, he'll think you'll win one in 3, so he thinks you'll pay $0.10 x 3 =$0.30 and get back $0.30.
If you want to sweeten the deal, and give him an "edge", tell him to put $0.25 under the cup. "Surely you must win! I'm a 1 in 3 chance of getting $0.25, so after 3 turns, on average, you'll get $0.30, and I'll only get $0.25 back!" - Pure rubbish, on average you'll get $0.50 back for $0.30 outlay. Try it just for fun with someone, and see if it doesn't work!