Thursday, March 8, 2012

A logic puzzle

Recently I finished reading The Math Gene, by Keith Devlin. Here's a logic puzzle from the book.


Imagine I lay four cards on a table in front of you. I tell you each card has a number on one side and a letter on the other. On the uppermost faces of the cards you see the four symbols:

E  K  4  7

I then tell you that the cards are printed according to the rule: If a card has a vowel on one side, it has an even number on the other side.

Your task: which cards do you have to turn over to be sure that all four cards satisfy this rule?

First one to post the correct answer gets a prize recognition.


Bobby and the Presidents said...

All four cards.

Anonymous said...

I pick E.
Rule states number conditional to vowel.
No rules stated on:
condition of number for a consonant
condition of letter for odd number
condition of letter for even number

Grubby said...

Must turn:
E - if no even number on reverse, in violation
7 - if vowel on reverse, in violation

(the K and 4 are irrelevant regarding the rule)

Craig M. Brandenburg said...

Grubby for the win!

The only way a card can be in violation is if it has a vowel on one side and an odd number on the other, so therefore you need to check only cards that show either a vowel or an odd number.