Quote:
Originally Posted by Green_Boy
hey guys i was watchin this movie the other day "21", in this a professor asks his student a question,it goes like this
In a game show we have 3 doors A,B,C behind one of the doors is a CAR and behind other 2 Ghost.
now the host asks u to select one of the door(remember u dont know what is behind what door) and say u select door A, now host tries to play a trick, as he know what is behind each door, he opens door C, and obviously there is a ghost behind the door, now if he asks u if u wish to change ur selection i.e . do u wish to go for B ?????????
what should u say to maximise ur chance of winning, should u go for B or should u stick to A???
in the movie they have told what u should do to maximise ur chances but they have not explained y.
think over it puys i know the answer as i have seen the movie  , but the best part is i know y it is so, i was thinking over it yesterday, so thought of sharing it with u guys
pour in ur answers, lets c if u can get it right!!!!
dont just post the answer, if possible post the explanation also and the probability for him to win 
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He has said in the movie that the probability of winning increases if the player taked the switch. Can be better explained like this.
There are 3 doors and there is a car behind one and 2 goats behind the other 2 doors. There can 3 kinds of plcaings 1)CGG 2)GCG 3) GGC
Lets consider each case assuming the player always opts for door1. Same can extended to all doors.
1) Player chooses 1. Host opens door 3
If swithced- loses
no switch - wins
* case remains same even if host opnes door 2
2)Player chooses door 1. host opens door 3
if switched - Wins
not switched - loses
3) player chooses door 1. Host opens door 2
If switched - wins
not switched - loses
In 3 cases he wins 2 if he switches his choice
In 3 cases he loses 2 if not switched.
Probablity increases if switched
( Host knows where the car is and he opens the door where there is a goat)