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Can you solve the frog riddle? - Derek Abbott


18,196 Questions Answered

TEDEd Animation

Let’s Begin…

You’re stranded in a rainforest, and you’ve eaten a poisonous mushroom. To save your life, you need an antidote excreted by a certain species of frog. Unfortunately, only the female frog produces the antidote. The male and female look identical, but the male frog has a distinctive croak. Derek Abbott shows how to use conditional probability to make sure you lick the right frog and get out alive.

Additional Resources for you to Explore

This frog riddle is an example of the use of conditional probability. That is when we calculate a probability of an event conditioned on another event taking place. Dig into another famous puzzle called the Monty Hall Problem here, which is also an exercise in conditional probability. Some more great examples are here.

These are cute puzzles that challenge us to think about how conditional probability works. However, what about actual applications in science, economics, medicine, criminology, and engineering?

In life, if we can use information to eliminate possibilities then we can target the answers we seek with greater probability. If we go on 10 dates there’s a 10% chance we’ll pick the best marriage partner out of them. But if information gained from the dates can definitely eliminate 8 of them, then we now have increased chance of hitching the best one to 50%.

A cold case detective seeks to eliminate unlikely and impossible scenarios to target the more likely suspect.

A stock market trader tries to use the information he knows about corporations and the current market to eliminate poorer trades and focus in on the ones more likely to succeed.

Engineers use the math of information and conditional probability when dealing with streams of digital information, such as 10000111001010110001001111… Given that our device receives, say, a “1”, if the next bit has a high probability of being also “1” then we are getting predictable content. If the next bit is surprising then the sequence is giving us something rich in information content. Using the math of conditional probability, engineers carefully design everything from the way bits are encoded on your DVD to the way they are encoded in a digital cellphone transmission.

And who would have thought all that high tech stuff had anything to do with a couple of frogs?

See if you can search the Internet and find five application examples from science, engineering, medicine, or forensics where calculations based on conditional probability are used.

Like the challenge of riddles? Start by taking a look at these three lessons and see how you do. Good luck!
Can you solve "Einstein’s Riddle"? - Dan Van der Vieren
The famously difficult green-eyed logic puzzle - Alex Gendler
Can you solve the prisoner hat riddle? - Alex Gendler

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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 Derek Abbott
  • Script Editor Alex Gendler
  • Director Outis
  • Narrator Addison Anderson

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