Can You Solve the Airplane Fuel Riddle?

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Here's a fun riddle: Professor Fukanō plans to circumnavigate the world in his new airplane. But the plane's fuel tank doesn't hold enough for the trip—in fact, it holds only enough for half the trip. But with the help of two identical support planes (which can refuel him in mid-air) piloted by his assistants Fugori and Orokana, the professor thinks he can make it in one trip. But since all three planes have the same problem of limited fuel, how can they work together to achieve the professor's goal without anyone running out of fuel?

This TED-Ed riddle is very much like a Popular Mechanics riddle written in 2016. It's a tricky one, and it helps to have a piece of paper handy.

It's explained in the video below (along with a "pause now" bit so you can solve it yourself). If you're not a fan of video, here are the starting rules:

1. The professor's plane must make a single continuous trip around the world without landing or turning around.

2. Each plane can travel exactly 1 degree of longitude in 1 minute for every kiloliter of fuel. Each can hold a maximum of 180 kiloliters of fuel.

3. Any plane can refuel any of the others in mid-air by meeting at the same point and instantly transferring any amount of fuel.

4. Fugori and Orokana's planes can turn around instantaneously without burning fuel.

5. Only one airport is available for any of the planes to land, take off, or refuel.

6. All three planes must survive the experiment, and none may run of fuel in mid-air.

As the video explains, the airport mentioned in point #5 happens to be on the equator.

Here's the video:

For a bit more from TED-Ed on this riddle, check out this lesson page. If you want to read a solution to a very similar puzzle without watching the video above, try this Math is Fun puzzle page.

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]

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