TED-ED: Can you solve the dark coin riddle? - Lisa Winer

In this video, a traveler finds a legendary dungeon with ancient coins but must solve a wizard's puzzle to escape. The puzzle involves separating coins into two piles with equal numbers of silver-facing coins, but the traveler is left in darkness. The solution is to move 20 coins and flip them, ensuring both piles have the same number of silver-facing coins. This works due to complementary events, where the number of silver and gold-facing coins in any 20-coin combination adds up to 20. The video explains the mathematical reasoning behind this solution, allowing the traveler to escape with the treasure.

What is the good news for the adventurer upon reaching the dungeon?

• The coins are made of chocolate.

• The dungeon is easy to escape.

• They found the legendary coins.

• The wizard will guide them out.

What challenge does the adventurer face in the dungeon?

• Building a bridge.

• Defeating a dragon.

• Solving a puzzle to leave.

• Finding a hidden key.

How many silver-facing coins did the adventurer count before the lights went out?

• 15

• 10

• 25

• 20

What is the first step in solving the coin puzzle?

• Ask the wizard for help.

• Flip all the coins.

• Move 20 coins aside.

• Count all the coins.

Why does flipping the 20 coins solve the puzzle?

• It reveals a hidden message.

• It changes the coin's weight.

• It ensures equal silver-facing coins in both piles.

• It makes all coins gold-facing.