Skip to main content

Can you solve the fortress riddle? - Henri Picciotto


1,334 Questions Answered

TEDEd Animation

Let’s Begin…

Bad news: your worst enemies are at the gate. Your fledgling kingdom guards the world’s only herd of tiny dino creatures. To you, they’re sacred. To everyone else, they’re food. The three closest nation-states have teamed up to smash open your walls and devour the herd. Can you build fortifications for your kingdom before the siege weapons arrive? Henri Picciotto shows how.

Additional Resources for you to Explore

You can find a guided exploration of this problem as “The McNuggets Problem” on Henri Picciotto’s Math Education Page.

The activity leads to a general formula for the largest impossible number (when it exists) in the case of two “building block” numbers.

Mathematicians know this problem as “the coin problem”. You can read about it here.

Want more puzzles? TED-Ed has lots of fun and challenging brainteasers in our Riddle Series!

Next Section »

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 Henri Picciotto
  • Director Igor Coric, Artrake Studio
  • Narrator Addison Anderson
  • Director of Production Gerta Xhelo
  • Producer Anna Bechtol
  • Editorial Director Alex Rosenthal
  • Associate Producer Sazia Afrin

More from Can You Solve This Riddle?