Maths Teaser

[Pintos]

This is an old one....

You're on a game show and the host shows you three doors (A,B and C), behind two of the doors is a goat, behind the third is a car. He asks you to choose a door and you choose (for example) door A.

The host opens door B and shows you a goat (he will always show you a goat behind one of the other doors).

He give's you the option of sticking with Door A or changing to Door C.

Do you stick or change and what are the probabilities that your dealing with?

Change to door C - 2/3 chance it's a car

 

[keithbeaky]

If anyone can explain the answer to this, I'd be grateful. It's been bugging me for ages now...

View attachment 32602

Paradox?

 

[Sergei's Celebration]

Paradox?

Na...more a Pink Coconut.

 

[leigull]

This is an old one....

You're on a game show and the host shows you three doors (A,B and C), behind two of the doors is a goat, behind the third is a car. He asks you to choose a door and you choose (for example) door A.

The host opens door B and shows you a goat (he will always show you a goat behind one of the other doors).

He give's you the option of sticking with Door A or changing to Door C.

Do you stick or change and what are the probabilities that your dealing with?

Always change, gives you an extra 1/3 of a chance

 

[Bold Seagull]

Have another look, there are 2 x 25%s therefore 25% can not be the answer; it should be 50% but getting the 50% answer is only a 25% chance...i think.

0%!

If anyone can explain the answer to this, I'd be grateful. It's been bugging me for ages now...

View attachment 32602

Answering at random means picking one of the four options without knowing what it is. As two of the options are 25%, then there is a 1 in 2 chance of picking one. There is a 1 in 4 chance of picking 50% or 60%.
So the answer is 50%

This. Mathmatical paradox. You have a 25% chance of picking the right answer, however 2 of the answers being 25% mean that is a 50% chance. If 50% is the correct answer, you only have a 25% chance of picking that. If you've only a 25% chance of picking the correct answer 50%, you've got a 50% chance of picking 25%.

Paradox?

 

[Acker79]

nevermind

 

[Shropshire Seagull]

Here's a tricky one:
What's the square root of -9 [minus-nine] ?

 

[jackanada]

Here's a tricky one:
What's the square root of -9 [minus-nine] ?

+3i or -3i

 

[Notters]

This. Mathmatical paradox. You have a 25% chance of picking the right answer, however 2 of the answers being 25% mean that is a 50% chance. If 50% is the correct answer, you only have a 25% chance of picking that. If you've only a 25% chance of picking the correct answer 50%, you've got a 50% chance of picking 25%.

Disagree, I'd say the answer is "it depends what the question is"

 

[sten_super]

This is an old one....

You're on a game show and the host shows you three doors (A,B and C), behind two of the doors is a goat, behind the third is a car. He asks you to choose a door and you choose (for example) door A.

The host opens door B and shows you a goat (he will always show you a goat behind one of the other doors).

He give's you the option of sticking with Door A or changing to Door C.

Do you stick or change and what are the probabilities that your dealing with?

I always find that one really difficult to explain to people, unless you generalise it up to 100 doors. Completely messes with our perceptions of probability.

 

[leigull]

I always find that one really difficult to explain to people, unless you generalise it up to 100 doors. Completely messes with our perceptions of probability.

Wiki explains it quite well: Monty Hall problem - Wikipedia, the free encyclopedia

In the Simple Solution section: "An even simpler solution is to reason that switching loses if and only if the player initially picks the car, which happens with probability 1/3, so switching must win with probability 2/3"

 

[sten_super]

Wiki explains it quite well: Monty Hall problem - Wikipedia, the free encyclopedia

In the Simple Solution section: "An even simpler solution is to reason that switching loses if and only if the player initially picks the car, which happens with probability 1/3, so switching must win with probability 2/3"

Yes, I'd just read that and was coming back to post it!

 

[SkankieBiscuit]

How about this one?

Me and my two flat mates were after a decent big new telly for the flat, and a mate of ours said he had seen a peach of an LED full HD 32 inch for exactly £300, and he could pick it up for us on his way home from work next day.

So in the pub that night we each gave him £100, so he could go out and buy the £300 TV.

He went to the shop, and to his delight the price had been reduced even further, to just £250. He obviously thought he would keep quiet about this further discount and pocket the £50 himself.

But his conscience got the better of him, so when he delivered the telly to us he said he got it for £250. And as £50wasn't easily divisible by 3 he said "how about I give you £10 back each, and I keep the other £20 for my trouble, time and petrol money?". And we all thought 'fair enough, he's done us a proper good turn here'.

So at the end of the day, we had each given him £100, but he had given each of us a tenner back. So each of us had parted with £90. Three times £90 is £270, add on the £20 he kept for himself, makes £290.

Hang on a minute, so where's the other tenner gone?

Your friend obviously pocketed £30 as opposed to the £20 if you say £50 off minus £10 to you and £10 to your friend he is infact pocketing £30 not £20. I thank you.

 

[Bold Seagull]

Disagree, I'd say the answer is "it depends what the question is"

Only politicians answer questions with a question!

 

[Albumen]

Change to door C - 2/3 chance it's a car

Yep but it still blows my mind.

 

[DavidinSouthampton]

There's a 0% chance of picking 0%, as that's not one of the options given.

Agree.
If you pick 25%, you are wrong, because there are two possibilities of choosing it, so the answer is 50%
If you pick 50%, you are wrong, because there is only 1 possibility of choosing it
It is therefore impossible to choose the right answer from the choices given.

Elementary, just in case there is anyone out there called Watson.

 

[Perkino]

Only politicians answer questions with a question!

Not true, a lot of teachers do that aswell

 

[folkestonesgull]

50% isnt it - you are either right or wrong.

 

[SeagullSongs]

"If you choose an answer to this question at random, what is the chance you will be correct?"

The word this implies that very sentence. As there are no options within the question itself it is impossible to say.
Also, minor semantics, the word chance should be replaced with probability.

If you take the options into consideration, the answer yet again depends entirely on what you state your answer as.
If I were to say A, B, C or D, then there is a 25% chance I am correct.
Were I to say one of the given percentages, it is impossible that my answer is correct.

 

[Brightonfan1983]

I never Googled this initially, but after reading your replies, had to.

http://www.quora.com/If-you-choose-an-answer-to-this-question-at-random-what-is-the-chance-you-will-be-correct-A-25-B-50-C-60-D-25

I'm gutted it's a paradox, unsolvable. Really thought there'd be an interesting quirky maths solution. Still, good to see NSC brains on show!