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The Fire Crystal Riddle and proof by contradiction

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Someone has tripped the magical alarms in the Element Temple. When you and the other monks arrive on the scene, you know you have a disaster on your hands. Four young apprentices broke into the temple’s inner chamber to steal the sacred element crystals. But when the alarm went off they panicked, and each of them swallowed a crystal. Can you determine who ate which crystal?

Everything changed when the fire crystal got stolen: Stop the video at 1m38s to try and solve the puzzle. Use the info below:

This TED-Ed puzzle can be solved by something called “proof by contradiction” or indirect proof, the method of figuring out what’s true by determining that it can’t be false. From

When proving something is true using proof by contradiction, you assume the statement to be false, and as you proceed with the proof, you run into a contradiction, making the assumption of your original statement being false impossible, thus it must be true.

When deciding if proof by contradiction is the best way to prove a given statement, it is a good idea to ask yourself, what would happen if the statement weren’t true?

Related reading: Reductio ad absurdum from Kiddle’s Kpedia and Proof by Contradiction at

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