I present to you a deck of 4 cards. Each card has on one side a letter of the alphabet, and on the other side a single digit from 0-9.
I propose a hypothesis that may apply to this deck:
If the letter is 'E', then the number on the other side is '4'.
I then drop the 4 cards on the table, and you see:
'B', '7', 'E', '4' (on the respective cards).
Which of the 4 cards must you turn over to verify or disprove my hypothesis?
You need to turn over two of the cards.
The hyposthesis is "If the letter is 'E', then the number on the other side is '4'"
NB: It does NOT say that if the number is 4 then the letter is E.
So, which cards?
B - no, not an E so we don't need to check for a 4.
7 - yes, we need to see if there is an E on the other side as this would disprove the hypothesis.
E - yes, we need to see if there is a 4 on the other side as this would disprove the hypothesis.
4 - no, we don't care if a 4 opposes any letter.
So we turn over E and 7.
Solution
