See the statement implies thatQuote:
You have 5 cards
You must prove the rul by turning over as few cards as possible.
the rule is : If the letter on side of a card is a vowel , the number on the other side is odd.
"if the *letter* on side of a card is a vowel, the *number*
on the other side is odd.
So the contrapositive of the statement is
If the *number* on side of a card is not odd, then the *letter* on side of a card is not a vowel.
So your right a "card" with one side a vowel and one side a letter
would not follow the rule. But it also would not meet the definition of a card because the rule assumes to that a card has a letter on one side and a letter on the other side.