I have four cards for you (each has a number on one side and a letter on the other side). One of the cards shows an E, one shows a 4 on one face, one has a K on one face, and one has a 7.
I say that a card with a vowel on one side (such as “E”) must show an even number on the other side.
My question to you is: Which card(s) do you need to turn over to see if I am telling the truth? And what’s the minimum number of cards you need to turn over in order to see if I am telling the truth?