See If You Can Solve This Tricky Coin-Flipping Riddle


Make sure your head is in working order before trying to solve this riddle from TED-Ed, because it's a stumper.

Here's the scenario: You're an explorer who's just stumbled upon a trove of valuable coins in a remote dungeon. Each coin has a gold side and a silver side, each with an identical scorpion seal. The wizard who guards the coins agrees to let you have them, but he won't let you leave the room unless you separate the hoard into two piles with an equal number of coins with the silver side facing up in each. You've just counted the total number of silver-side-up coins—20—when the lights go out. In the dark, you have no way of knowing which half of a coin is silver and which half is gold. How do you divide the pile without looking at it?

As TED-Ed explains, the task is fairly easy to complete, no psychic powers required. All you need to do is remove any 20 coins from the pile at random and flip them over. No matter what combination of coins you choose, you will suddenly have a number of silver-side-up coins that's equal to whatever is left in the pile. If every coin you pulled was originally gold-side-up, flipping them would give you 20 more silver-side-up coins. If you chose 13 gold-side-up coins and seven of the silver-side coins, you'd be left with 13 silver coins in the first pile and 13 silver ones in your new stack after flipping it over.

The solution is simple, but the algebra behind it may take a little more effort to comprehend. For the full explanation and a bonus riddle, check out the video from TED-Ed below.

[h/t TED-Ed]

How Many of These 15 General Knowledge Trivia Questions Can You Get Right?

Feeling Stressed? Playing Tetris Could Help Relieve Your Anxiety


When Nintendo released their handheld Game Boy system in the U.S. and Japan in 1989, the first game most users experimented with was Tetris. Bundled with the system, the clever puzzler—which prompts players to line up a descending array of tiles to create horizontal lines—was the video game equivalent of an addictive drug. Some players described seeing the shapes in their dreams. The game was in the hands of 35 million portable players; by 2010, it had sold 100 million smartphone downloads.

Now, there’s evidence that Tetris players may have a solution to anxiety in the palms of their hands. According to a paper published in the journal Emotion, Tetris has the capability to relieve stress and troubling thoughts by providing a form of distraction.

As part of a larger study about the benefits of distraction, researchers at the University of California, Riverside conducted an experiment on 309 college students who were told to expect some anxiety-provoking news: They were told someone would be offering an evaluation of their physical attractiveness. While they waited for their results, a third of the subjects played a slow-moving, beginner-level version of Tetris; another group played a high-speed variation; and a third played an adaptive version, which automatically adjusted the speed of the game based on the player’s abilities.

Tetris games that were too slow or too fast bored or frustrated players, respectively. But the game that provided a moderate challenge helped reduce the subjects’ perception of their stress levels. They reported a quarter-point higher level of positive emotions on a five-point scale and a half-point reduction of negative emotions. The students still worried about the results of the attractiveness evaluation, but they experienced fewer negative feelings about it.

The key, according to the study, is that the students were experiencing “flow,” a state of mind in which you’re so engrossed in an activity that you lose your sense of self-awareness. While Tetris may be one of the best ways to quickly fall into flow, anything that consumes your attention—playing music, drawing, cooking—is likely to work.

The next time you have to wait for potentially life-altering news, you may find that a Tetris session will help you cope.

[h/t NPR]