Card Hypothesis

Only the cards have changed

We’ve done this before.
But do you remember which cards must be turned over and why?

FACT: Each card has a number on one side and a letter on the other.
HYPOTHESIS: Every card that has a vowel on one side has an even number on its opposite side.

THE TEST: Which card or cards must you turn over in order to test the Hypothesis?

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The 15 possible answers are:

All four cards: G 2 3 E
Three cards: G 2 3 / G 2 E / G 3 E / 2 3 E
Just two cards: G and 2 / G and 3 / G and E / 2 and 3 / 2 and E / 3 and E
Just one card: Card G only / Card 2 only / Card 3 only / Card E only