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Can you solve the locker riddle? - Lisa Winer


8,416 Questions Answered

TEDEd Animation

Let’s Begin…

Your rich, eccentric uncle just passed away, and you and your 99 nasty relatives have been invited to the reading of his will. He wanted to leave all of his money to you, but he knew that if he did, your relatives would pester you forever. Can you solve the riddle he left for you and get the inheritance? Lisa Winer shows how.

Additional Resources for you to Explore

The locker problem is often used as an introduction to factors, multiples, square numbers, prime numbers, and sequences. It shows that some problems can be solved using a smaller, simpler problem rather than brute force (also known as the method of exhaustion). Here is a more detailed video solution to the locker problem, and here is a related problem that uses Othello pieces instead of lockers.

If you enjoyed the locker problem, you might enjoy studying figurate numbers. Another fun problem to investigate is the handshake problem. An interesting extension is to write square numbers as the sum of odds. Visit the educator's blog that links these units together, and another that is from the viewpoint of students who learned about it.

Love riddles? TED-Ed has plenty of them that will challenge you:

The famously difficult green-eyed logic puzzle - Alex Gendler

Can you solve the prisoner hat riddle? - Alex Gendler

Can you solve "Einstein’s Riddle"? - Dan Van der Vieren

Can you solve the temple riddle? - Dennis E. Shasha

Can you solve the frog riddle? - Derek Abbott

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About TED-Ed Animations

TED-Ed Animations feature the words and ideas of educators brought to life by professional animators. Are you an educator or animator interested in creating a TED-Ed Animation? Nominate yourself here »

Meet The Creators

  • Educator Lisa Winer
  • Director Outis
  • Narrator Addison Anderson

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