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Can You Solve the Virus Riddle?

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In this video riddle, you're a researcher who needs to solve a math problem. The fate of humanity is at stake!

Here's the setup. Your research group has isolated a lethal virus and is studying it in a lab. But one night after you leave the lab, an earthquake strikes and breaks the virus vials. This means that 15 of the 16 rooms in the lab are contaminated, and you have to get past the lab's security system in order to destroy the virus. (There is time pressure, as eventually the virus will escape the lab and kill us all!)

The lab is built as a 4x4 grid, containing a total of 16 rooms, with an entrance at the northwest corner and an exit at the southeast corner. Each room is connected to the adjacent rooms by an airlock. Only the entrance and exit rooms are connected to the outside. The virus has been released in every room except the entrance room.

To destroy the virus samples, you must enter each room and pull its self-destruct switch, destroying the room and the virus within it. But there's a problem—because the lab is in lockdown mode, once you enter a contaminated room, you can't exit without activating the self-destruct switch. Furthermore, once the self-destruct switch has been activated, you cannot re-enter a contaminated room.

Your job is to enter through the entrance room, exit through the exit room, and destroy the virus in every contaminated room. How can you do it?

From the video (at the 1:41 mark), here are the official rules and restrictions:

1. You must enter the building through the entrance and leave through the exit.

2. Every room except the entrance is contaminated.

3. Once you enter a contaminated room, you must pull the switch.

4. After pulling the switch, you must immediately leave the room.

5. You cannot return to a room after its switch has been activated.

Watch the video below for a visual explanation of the problem. This one's a bit of a forehead-smacker when you see the solution.

For more on this puzzle (and its solution), check out this TED-Ed page.

Note: If you're interested in math (without puzzle spoilers), this problem is related to Hamiltonian Paths, or paths that visit each point exactly once.

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History
When Math Discoveries Led to Banned Numbers
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The literature world has seen more than its share of controversy. The best stories tend to provoke the strongest reactions—both positive and negative—in readers, which is why so many classic books have been banned at one point or another. But even a more objective field like math isn’t immune to conflict. In its new video, TED-Ed rounds up the numbers that caused such a stir when they were introduced that they were banned in math circles.

One of the earliest examples comes from ancient Greece. A mathematician named Hippasus was having trouble solving certain equations with fractions and whole numbers alone, so he came up with irrational numbers to make these values easier to express. The ruling school of thought at the time dictated that everything in nature could be explained elegantly with the numbers that already existed. Threatened by Hippasus’s new notion, his fellow mathematicians rejected the irrational numbers and had him exiled.

Other numbers have been banned for legal reasons. When Arab traders brought their positional number system, which included zero, to Italy in the Middle Ages, Florence banned it from record-keeping fearing that they would be easier to forge than Roman numerals. The Arabic way of counting also led to the rise of negative numbers, which were regarded with disdain by many experts into the 19th century. For more banned numbers, including some that are prohibited today, check out the full story below.

[h/t TED-Ed]

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Euclid
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Live Smarter
An Ex-Google Engineer Just Reinvented the Measuring Cup
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Euclid

Recognizing a problem most people didn’t even know they had, former Google and Facebook software engineer Joshua Redstone has made a bold claim for his recent Kickstarter venture: He’s developed a better measuring cup.

According to the Boston Business Journal, Redstone spent four years tinkering with a solution to something that had long annoyed him as an amateur chef: Traditional measuring cups, which are stocky and not very well tapered, don’t do a great job of accurately measuring their own contents. Redstone believes the shape of a cup determines its success, particularly when a cook overfills a liquid or solid by a tiny amount. The smaller the volume, the more the problem is magnified.

Euclid

Redstone’s cup, Euclid, resolves the issue. According to the Kickstarter page: “With traditional measuring cups, the smaller the amount, the harder it is to measure accurately. The culprit? The shape. Straight sides magnify errors when measuring lower down in the cup. Some have tried to solve this problem with conical measuring cups, but their results fall short of Euclid’s by up to 60 percent. Euclid is the only measuring cup with a mathematically optimal, tapered design for consistent accuracy across amounts.”

Euclid is just about ready to overshoot its $30,000 Kickstarter goal. Backers can pay $24 for the cup now, or wait until it’s available at retail for a slightly higher price to be determined. The cup is scheduled for release in May 2018.

[h/t Boston Business Journal]

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