Tanya Khovanova's Math Blog

Every year I review MIT mystery hunt from a mathematician’s point of view. I am way behind. The year is 2020, but I still didn’t post my review of 2019 hunt. Here we go.

Many puzzles in 2019 used two data sets. Here is the recipe for constructing such a puzzle. Pick two of your favorite topics: Star Trek and ice cream flavors. Remember that Deanna Troi loves chocolate sundae. Incorporate Deanna Troi into your puzzle to justify the use of two data sets.

On one hand, two data sets guarantee that the puzzle is new and fresh. On the other hand, often the connection between two topics was forced. Not to mention that puzzle solving dynamic is suboptimal. For example, you start working on a puzzle because you recognize Star Trek. But then you have to deal with ice cream which you hate. Nonetheless, you are already invested in the puzzle so you finish it, enjoying only one half of it.

Overall, it was a great hunt. But the reason I love the MIT mystery hunt is because there are a lot of advanced sciency puzzles that can only appear there. For example, there was a puzzle on Feynman diagrams, or on characters of representations. This year only one puzzle, Deeply Confused, felt like AHA, this is the MIT Mystery hunt.

Before discussing mathy puzzles I have to mention that my team laughed at Uncommon Bonds.

I will group the puzzles into categories, where the categories are obvious.

Mathy puzzles.

• Bubbly—Combinatorial game theory.
• Rules of Order—Fractals mixed with movies.
• Cubic—A long list of cubic polynomials with integer coefficients.
• Twisty Passages—Famous number properties that remind my of my Number Gossip website.

Here are some logic puzzles, in a sense that Sudoku is a logic puzzle.

• Lantern festival—A cool mixture of Slitherlinks and Galaxies.
• Invisible Walls.
• Place Settings.
• Middle School of Mines—Minesweeper.
• Moral Ambiguity—Nonograms with a twist.
• Connect Four—Mastermind. There was a strong hint that the extraction step was also mastermind. My team spent some time trying to mastermind the ending, until we backsolved. The extraction step was not mastermind. The final grid in the puzzle had the word CODE written in red. It corresponded to letters CDEO found at that location. Given that the letters were not in alphabetical order, it gave the ordering, which didn’t exist in the puzzle. Anyway, you can see that I have a grudge against this puzzle. This could have been a great puzzle. But it wasn’t.
• Schematics—Tons of Nikoli puzzles of different types.

Now we have logic puzzles or another type, where you need to draw a grid. These are puzzles of the type: Who lives in the White House?

• Compromised.

Now we have logic puzzles or yet another type, where you need to figure out which statements are true and which are false.

• True and False².

Now some cryptography.

• Tales From The Crypt.
• You’re Gonna Need a Bigger Gravy Boat.
• The Bill.
• Helvetica Is Only an Okay Font.
• A Good Walk Spoiled—Some decyphering and Vim.
• Have You Seen Me?
• Chain of Commands.
• Picture Book.

And some programming.

• Turtle Power!

Miscellaneous.

• Hexed Adventure II: Hexed Again!—A text adventure game with a lot of logic.
• Loaded—Dice of different shapes.
• The Lives of Π—Large numbers.
• Battle of the Network Stars—A lot of actors in a grid.

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Every day I check coronavirus numbers in the US. Right now the number of deaths is 288 and the number of recovered is 171. More people died than recovered. If you are scared about the mortality rate, I can calm you and myself down: our government is incompetent—the testing wasn’t happening—that means the numbers do not show people who had mild symptoms and recovered. The real number of recovered people should be much higher.

Scientists estimated the mortality rate of coronavirus as being between 1 and 3.5 percent. Also, they say that it usually takes three weeks to die. That means three weeks ago the number of infected people in the US was between 8,000 and 29,000. The official number of cases three weeks ago was 68. I am panicking again—our government is incompetent—three weeks ago they detected between 0.25 and 1 percent of coronavirus cases. If this trend continues, then the official 19,383 infected people as of today means, in reality, somewhere between 2 million and 8 million infected people.

I can calm you and myself down: the testing picked up pace. This means, the ratio of detected cases should be more than 1 percent today. Probably the number of infected people today in the US is much less than 8 million. I am not calm.

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My former student, Dai Yang, sent me the following cute puzzle:

Puzzle. You are playing a game with the Devil. There are n coins in a line, each showing either H (heads) or T (tails). Whenever the rightmost coin is H, you decide its new orientation and move it to the leftmost position. Whenever the rightmost coin is T, the Devil decides its new orientation and moves it to the leftmost position. This process repeats until all coins face the same way, at which point you win. What’s the winning strategy?

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