Cards!Logic Level 3
Say we have a deck of 14 cards. They have a letter on one side, and a number on the other. Face up, they are: \[1,2,3,4,5,6,7,A,B,C,D,E,F,G.\] Let's propose that on the back of any vowel card, there must be a prime. Find the minimum number of cards that must be flipped over to guarantee the validity of this statement.