A Stressful Game

A puzzle by Ezra Brown and James Tanton:

Three gnomes sit in a circle. An evil villain puts a hat on each gnome’s head. Each hat is either rouge or puce, the color chosen by the toss of a coin. Each gnome can see the color of his companions’ hats but not of his own.

At the villain’s signal, all three gnomes must speak at once, each either guessing the color of his own hat or saying “Pass.” If at least one of them guesses correctly and none guesses incorrectly, all three gnomes will live. But if any of them guesses incorrectly, or if all three pass, they’ll all die.

They may not communicate in any way during the game, but they can confer beforehand. How can they arrange a 75 percent chance that they’ll survive?

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Each gnome will pass unless he sees that both of his companions are wearing hats of the same color. In that case he will guess the opposite color. This produces a win in six of the eight possible arrangements of hats. (Ezra Brown and James Tanton, “A Dozen Hat Problems,” Math Horizons 16:4 [April 2009], 22-25.)

August 27, 2020August 26, 2020 | Puzzles

Black and White

glass chess problem

By F.G. Glass, 1903. White to mate in four moves. (Easier than it sounds.)

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If the white king just circles the pawn, all Black’s moves are forced: 1. Kf1 Kd2 2. Kf2 Kd1 3. Ke3 Ke1 4. Rc1#

August 15, 2020August 14, 2020 | Puzzles

Inside Business

A puzzle from MIT Technology Review, September-October 1999: A popular pastime at Bell Labs in the 1970s was to identify a word that contains a given string of letters — for example, OOKKEE is found in BOOKKEEPER. Michael Foster found English words that contain HIPE, HCR, and UFA. What are they?

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ARCHIPELAGO, WITCHCRAFT, and MANUFACTURE.

August 6, 2020August 5, 2020 | Language · Puzzles

Podcast Episode 300: Lateral Thinking Puzzles

Here are six new lateral thinking puzzles — play along with us as we try to untangle some perplexing situations using yes-or-no questions.

See full show notes …

June 22, 2020June 29, 2020 | Podcast · Puzzles

Black and White

healey chess problem

By Frank Healey. White to mate in two moves.

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With the quiet 1. Qa1! White threatens to push his pawn, giving mate. Black can stop this only with 1. … c4, and then the queen can mate from a5. From A Collection of Two Hundred Chess Problems, 1866.

March 26, 2020March 26, 2020 | Puzzles

Secret Message

Jonathan Swift’s Journal to Stella, a collection of 65 letters written to his friend Esther Johnson, contains some puzzling passages, such as this one:

“He gave me al bsadnuk lboinlpl dfaonr ufainfbtoy dpionufnad, which I sent him again by Mr. Lewis.”

How should the obscured phrase be read?

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“A bank bill for fifty pound.” It’s a null cipher in which alternate letters are ignored. (From David Kahn’s The Codebreakers.)

March 24, 2020March 23, 2020 | Literature · Puzzles

No Comment

Areas from r/blackmagicfuckery

March 16, 2020March 17, 2020 | Puzzles

Black and White

shinkman chess problem

By William Anthony Shinkman. White to mate in two moves.

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1. Ra2! wins. By withdrawing the rook along the second rank, White keeps the black queen pinned, so she must follow it along that rank. (Black has no other options — his only other legal move, 1. … h3, loses to 2. Nf3#.) No matter which square she chooses, 2. Bb8 is mate. Note that White must withdraw the rook all the way to the a-file in order for this to work. If it stops at any other square on the second rank, then the queen can capture it and find herself free to block (or capture) the checking bishop, escaping mate in two. From Cumming’s Souvenir Chess Board, 1886.

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March 9, 2020March 9, 2020 | Puzzles

Take 5

An interesting problem from Crux Mathematicorum, March 2004: The increasing sequence 1, 5, 6, 25, 26, 30, 31, 125, 126, … consists of positive integers that can be formed by adding distinct powers of 5. That is, 1 = 5⁰, 5 = 5¹, 6 = 5⁰ + 5¹, and so on. What’s the 75th integer in this sequence?

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Write the sequence in base 5: 1, 10, 11, 100, 101, 110, … Now if we consider these expressions as a sequence of binary numbers, then the number in position n is just n — if we convert the sequence from binary to base 10 it’s just 1, 2, 3, 4 … 75 in binary is 1001011, so the number we want is 5⁶ + 5³ + 5 + 1 = 15,756. (“Mathematical Mayhem,” Crux Mathematicorum 30:2 [March 2004], 72-76.)

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March 3, 2020March 2, 2020 | Puzzles

Black and White

From Theophilus A. Thompson’s Chess Problems, 1873. White to mate in two moves.

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1. Ba8! and the queen will mate.

February 19, 2020February 18, 2020 | Puzzles