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# Mathematic question

• Bronze
Joined: 14.02.2008
It is question to asked in the film 'Twenty one' and many of you, probably, are know the answer. If you know answer, please, do not wright it.

Question: You are in the show, and can win prize. It is be contained in the one door from three (1,2 or 3 for clarity). Showman know, where prize is be.
Showman is make a proposal you make choose door, when prize is be. For example, you selected door with number one. Then showman open door, then prize is out and make a proposal you change the door or keep you first choice.
What you do: change door, keep you first door, or it's all the same?
• 12 replies
• Bronze
Joined: 30.12.2010
The movie is 22? Or 21? I know the answer, but won't ruin fun.. Even though google could ruin it
• Bronze
Joined: 12.10.2011
Haven't seen the movie but I know the answer already (general math problem)

It's a really interesting problem to solve though
• Bronze
Joined: 14.02.2008
Originally posted by 4empion
It is question to asked in the film 'Twenty two' and many of you, probably, are know the answer. If you know answer, please, do not wright it.

Question: You are in the show, and can win prize. It is be contained in the one door from three (1,2 or 3 for clarity). Showman know, where prize is be.
Showman is make a proposal you make choose door, when prize is be. For example, you selected door with number one. Then showman open door, then prize is out and make a proposal you change the door or keep you first choice.
What you do: change door, keep you first door, or it's all the same?
Movie '21'
• Bronze
Joined: 01.05.2012
Ah, the famous Monty Hall problem.

Yeah, I know the answer.
• Super Moderator
Super Moderator
Joined: 02.09.2010
In the classic Monty Hall problem, one prize is valuable, the other two are much less valuable.
Let's say a car, and two goats.

No matter which door you pick, the showman always opens a door showing a goat, then asks "Do you want to change your choice?"

Do you change or keep your original choice?

I, too know the answer, but I'm no longer able to explain why it is correct.

There is a good wikipedia article on this, if anyone else gives up.
A link in the references points to "The Game Show Problem" which contains the original article in Parade magazine where is was purportedly first analysed.
Search for "Monty Hall problem"

Monty Hall was the host of "Let's make a deal" a game show in the US and ran from '63 to '77. It has apparently been resurrected.

Cheers,
--VS
• Bronze
Joined: 01.05.2012
What about all the people who don't know the answer for sure?

C'mon guys, give it a shot!
• Bronze
Joined: 30.12.2010
It's not that hard to find the answer online, it's hard to explain it, I'm not even sure if the answer given in movie can be scientifically supported.. As V said, no quality articles about it on wikipedia or similar pages..
• Bronze
Joined: 01.05.2012
Originally posted by FFRRAANNKKIIEE
It's not that hard to find the answer online, it's hard to explain it, I'm not even sure if the answer given in movie can be scientifically supported.. As V said, no quality articles about it on wikipedia or similar pages..
There definitely is a mathematical explanation behind it. It's actually quite simple, but counter-intuitive nonetheless, which is why many people initially have problems with it.
Shall we solve and explain it already?

For those of you who are curious about the answer and the logic behind it but want to figure it out on their own, feel free to re-enact this riddle with three playing cards (e.g. find the ace). The solution should soon become obvious.
• Super Moderator
Super Moderator
Joined: 02.09.2010
Originally posted by FFRRAANNKKIIEE
It's not that hard to find the answer online, it's hard to explain it, I'm not even sure if the answer given in movie can be scientifically supported.. As V said, no quality articles about it on wikipedia or similar pages..
Sorry I left that impression -- there are lots of good articles on this problem on wikipedia and elsewhere. Just google "Monty Hall problem"

The problem is based on the game show "Let's Make a Deal" whose original host was Monty Hall.

In the math problem, though, there is a wrinkle:
The showman always opens a door that has the crappy "prize". In the original game show, the 3 prizes were different, in the problem there is 1 good prize and two crappy ones.

The original problem had them as a car behind one door and a goat behind each of the others.

No problem at all if you'd rather have a goat

--VS
• Basic
Joined: 27.03.2014
Originally posted by TinoLaan
Haven't seen the movie but I know the answer already (general math problem)

It's a really interesting problem to solve though
this, but as a math wizard I dont find Monty Hall problem as a interesting to solve tho.

It's wayyy more interesting this:

The riddle: 100 prisoners are in solitary cells, unable to see, speak or communicate in any way from those solitary cells with each other. There's a central living room with one light bulb; the bulb is initially off. No prisoner can see the light bulb from his own cell. Everyday, the warden picks a prisoner at random, and that prisoner goes to the central living room. While there, the prisoner can toggle the bulb if he or she wishes. Also, the prisoner has the option of asserting the claim that all 100 prisoners have been to the living room. If this assertion is false (that is, some prisoners still haven't been to the living room), all 100 prisoners will be shot for their stupidity. However, if it is indeed true, all prisoners are set free. Thus, the assertion should only be made if the prisoner is 100% certain of its validity.

Before the random picking begins, the prisoners are allowed to get together to discuss a plan. So ---- what plan should they agree on, so that eventually, someone will make a correct assertion?

Q: How can the prisoners tell, with certainty, that all 100 of them have visited the central living room with the light bulb.
• Bronze
Joined: 02.09.2009
Are those prisoners able to see if the light in the living room is on from their cells? You only mentioned that they cannot see the light bulb in specific and (the prisoner who is in there I guess).