<< This statement makes no mention of how large the "set" of cards is, and only states that 4 are presented. Therefore, there is no way to test the assertion that vowels are ALWAYS paired with odd numbers other than checking all vowels in the entire unknown quantity of cards. >>
I think formatc: is absolutely correct when he said the above. so there's a loophole in your directions, maybe you can change it to:
<< The following set of cards has letters on one side, and numbers on the other side. You are told that vowels are always paired with odd numbers. Which cards must be turned over to test this assertion? >>