Firebox Card: Number 123: Difference between revisions

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(Alternate (maybe simpler) explanation.)
 
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Between all the distractions and parties at university. I did manage to fit in a few  
Between all the distractions and parties at university, I did manage to fit in a few  
experimental psychology lectures. One of the most interesting things i learned was how  
experimental psychology lectures. One of the most interesting things I learned was how  
at heart, people arent as logical as they think. Try this problem:  
at heart, people aren't as logical as they think. Try this problem:  


Each of these cards has a letter (A or K) on one side and a number (2 or 7) on the reverse.  
Each of these cards has a letter (A or K) on one side and a number (2 or 7) on the reverse.  
If i told you there was a rule stating that a card with A on one side will have a 2 on the  
If I told you there was a rule stating that a card with A on one side will have a 2 on the  
reverse, which two cards would you turn over to find out if the rule was true
reverse, which two cards would you turn over to find out if the rule was true?
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The answer is A and 2. [[image:green_123.jpg|thumb|Pack of Cards]]
The answer is A and 7. [[image:green_123.jpg|thumb|Pack of Cards]]
 
Some people guess the answer is A and 2. The logical statement of the problem can be phrased "an A on one side implies there will be a 2 on the other." People who get the answer wrong also presume the converse is true, that "a 2 on one side implies there will be an A on the other." This is not the case; therefore the 2 does not need to be checked. Another way to see this is that the statement can be phrased "no card has an A on one side and a 7 on the other side".

Latest revision as of 15:57, 4 December 2005

Illogical

From the firebox advert. The card on the top of the advert contains the following text:

Between all the distractions and parties at university, I did manage to fit in a few 
experimental psychology lectures. One of the most interesting things I learned was how 
at heart, people aren't as logical as they think. Try this problem: 

Each of these cards has a letter (A or K) on one side and a number (2 or 7) on the reverse. 
If I told you there was a rule stating that a card with A on one side will have a 2 on the 
reverse, which two cards would you turn over to find out if the rule was true?

The cards displayed on the card are

A K 2 7

The answer is A and 7.

Pack of Cards

Some people guess the answer is A and 2. The logical statement of the problem can be phrased "an A on one side implies there will be a 2 on the other." People who get the answer wrong also presume the converse is true, that "a 2 on one side implies there will be an A on the other." This is not the case; therefore the 2 does not need to be checked. Another way to see this is that the statement can be phrased "no card has an A on one side and a 7 on the other side".