CLOSE
Getty Images
Getty Images

Can You Solve the Frog Riddle?

Getty Images
Getty Images

In this riddle from TED-Ed, you're in a sticky situation. You're stranded in a rainforest and have accidentally eaten a poisonous mushroom. To survive the poison, you need to lick a very particular frog. But which frog is it?

You can watch the video below for more details, or read this description. The problem is simple: You are poisoned and you know that a particular species of frog produces the antidote, which will cure you if you lick it. But to make things more complex, you know that only female frogs of the species have the antidote—males do not. In this frog species, males and females look identical but males have a distinctive croak. (Males and females also occur in identical proportion in this species.) In one direction, you see a single frog. In another, a group of two frogs sitting together.

From the direction of the two frogs, you hear that distinctive "male frog" croak. Uh-oh! One of those two is definitely male.

As the poison sets in, you have to make a logical decision. You need to find a female frog with the antidote. Are your odds better going toward the group of two (one of which is definitely male), or toward the single unknown frog? And what are those odds, anyway?

Note that in this riddle you are not guaranteed to survive. You're just trying to take your best shot.

So which to choose, and why?

Watch the video below for a discussion of the problem and how the math stacks up behind one of the choices.

For more resources, consult this TED-Ed page. Once you've solved it (or if you've given up), you might also be interested in this related math problem.

nextArticle.image_alt|e
iStock
arrow
Health
The Math Behind the Classic Eye Chart Is Surprisingly Complex
iStock
iStock

Next time you're forced to take a vision exam at the DMV, take a moment to appreciate the complex math that went into the eye chart. What seems like a fairly straightforward way to assess eyesight is actually the result of specific calculations that can tell you a lot about how the human eye works.

As The Verge explains in the video below, eye charts measure one aspect of healthy vision: visual acuity. This is our ability to make out fine details in our surroundings—kind of like the resolution of a computer screen, but instead of pixels, it's measured in degrees. It's easy for our eyes to tell the difference between two points of light coming from different directions, but if those points start to move closer together they will eventually blur into one. The angle created just as two lines of light become too close for our eyes to distinguish them is called the resolution limit. In healthy adults, it measures one-sixtieth of a degree, or one arcminute wide.

When a doctor asks you to read an eye chart, the resolution limit is what they're looking for. The letters in the middle of an eye chart are all designed to be exactly one arcminute thick. If your vision is sharp, you should be able tell the difference between the white spaces and the black lines of the text from 20 feet away. 

A perfect 20/20 score on an eye chart test doesn't mean you have perfect vision: Visual acuity, along with color, contrast, and depth perception, are all important parts of healthy eyesight. And a higher resolution limit isn't always a sign of a permanent problem: For people who spend their days staring at a screen, it may be caused by the eye fatigue brought on by Computer Vision Syndrome. If this is a problem for you, here are some ways to tweak your behavior.

[h/t The Verge]

nextArticle.image_alt|e
iStock
arrow
fun
Could You Pass the Mensa Intelligence Test?
iStock
iStock

The biggest perk of being in Mensa just might be the bragging rights. Membership is reserved for society’s most elite intellectuals, and the only path to induction is to score in the 98th percentile or higher on their notorious IQ test. Think you have the smarts to join the top .0001 percent of thinkers? Before you apply for the real thing, flex your brain by answering a few sample questions from the test.

The practice questions shared on Popular Science cover the skills Mensa looks for in its members: verbal, spatial, and mathematical reasoning. To ace the test, you’ll need to be just as capable of recognizing obscure vocabulary as you are of doing complex math in your head.

The real Mensa IQ test is really two tests: a timed test with 50 questions and one with seven sections. (Scoring in the 98th percentile on either test qualifies you to join.) Answering all four of the questions posted to PopSci correctly doesn’t necessarily mean you’re intelligent enough for Mensa, but it should give you a confidence boost if you’re thinking about applying. If you do miss a question or two, maybe hold off on taking the official test until you’ve had more time to prepare: Scoring below the 98th percentile bars you from joining the exclusive club for life. You can take the practice test now by heading over to PopSci.

[h/t Popular Science]

SECTIONS

arrow
LIVE SMARTER
More from mental floss studios