Logic test answer

A

B

6

7

 

Card A: if it has an even number on the other side, the theory is wrong

Card 6: if it has a vowel on the other side, the theory is wrong.

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Not needed:

Card B: Consonants could have odd or even numbers without affecting the theory.

Card 7: Odd numbers could have vowels or consonants without affecting the theory.

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When I first came across this test in the 1970s, about 10% of graduates got it right. I would guess that people tend to look for proof that a theory is right, but not for evidence that it is wrong.