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 Formal Reasoning (Posted on 2004-12-15)
I present to you a deck of 4 cards. Each card has on one side a letter of the alphabet, and on the other side a single digit from 0-9.

I propose a hypothesis that may apply to this deck:
If the letter is 'E', then the number on the other side is '4'.

I then drop the 4 cards on the table, and you see: 'B', '7', 'E', '4' (on the respective cards).

Which of the 4 cards must you turn over to verify or disprove my hypothesis?

 See The Solution Submitted by SilverKnight Rating: 3.0000 (22 votes)

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 re(3): Solution | Comment 49 of 60 |
(In reply to re(2): Solution by Sean)

If you turned over the 7, there might be an E on the back.  That would disprove the hypothesis.

And what they were saying before wasn't "If E, then 4, therefore: If 4, then E".  Using your example about squares being quadrilaterals, but not all quadrilaterals being squares:

If a shape is a square, it is definitely a quadrilateral.
If a shape is not a quadrilateral, then it is definitely not a square

So, if you have a number that isn't a 4, an E cannot be on the back, and you must look under the 7 to make sure.

Edited on March 6, 2005, 11:20 pm
 Posted by Dustin on 2005-03-06 23:14:23

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