Nob’s Number Puzzle

nob's number puzzle

A conundrum by the late brilliant Japanese puzzle maven Nob Yoshigahara.

Lee Sallows writes, “You have to solve this yourself, otherwise you won’t see how beautiful it is.”

April 30, 2014April 29, 2014 | Puzzles

Black and White

petkovic chess problem

A cylindrical problem by Miodrag Petkovic: Imagine that the board is rolled into a cylinder, with the a-file adjoining the h-file. How can White mate in two moves?

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1. Nb5! Kxb5 2. Qa4#. If 1. … Kd5 then 2. Qe6#. From Mathematics and Chess, 1997.

April 25, 2014May 4, 2014 | Puzzles

Black and White

griswold chess problem

By John Griswold White. White to mate in two moves.

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The quiet 1. Kg5! forces Black to move a knight, permitting White to mate from e6 or g6. (Note that 1. Ke5 won’t work because of 1. … Nc6+!) From Canadian Illustrated News, 1880.

April 18, 2014April 27, 2014 | Puzzles

No Attraction

Kepler’s second law holds that a line segment connecting an orbiting planet to its sun sweeps out equal areas in equal periods of time: In the diagram above, if the time intervals t are equal, then so are the areas A.

If gravity were turned off, would this still be true?

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Yes. The planet would pass into space in a straight line, and each time interval would define a triangle with height h and base t. Since a triangle’s area is half the product of its height and base, these are all equal.

April 12, 2014March 5, 2015 | Puzzles · Science & Math

Black and White

loyd chess problem

By Sam Loyd. White to mate in two moves.

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Typically for Loyd, the answer is the least likely move on the board: 1. Nd2! (threatening 2. Rxe2#) If 1…Kxf2 then 2.Qg3# If 1…Kxd2 then 2.Qc3# If 1…Rxe3 then 2.Qxe3#

April 11, 2014April 20, 2014 | Puzzles

Math Notes

Prove that log₁₀ 5 is irrational.

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Suppose it’s rational. Then log₁₀ 5 = a/b, where a and b are positive integers. Then 10^a/b = 5 and 10^a = 5^b. But these two values can never be equal — any positive integral power of 10 will end in 0, and any such power of 5 will end in 5. So log₁₀ 5 cannot be rational.

April 10, 2014April 13, 2014 | Puzzles

Black and White

carpenter chess problem

By George Edward Carpenter. White to mate in two moves.

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1. Qh2! threatens 2. Nf5#. If 1. … Kf4 then 2. Ne4#, and if 1. … Kd4 then the queen mates from h8. From The Chess Players’ Chronicle, 1874.

April 4, 2014April 13, 2014 | Puzzles

The Suicidal King

Imagine a 1000 x 1000 chessboard on which a white king and 499 black rooks are placed at random such that no rook threatens the king. And suppose the king goes bonkers and wants to kill himself. Can he reach a threatened square in a finite number of moves if Black is trying actively to avoid this?

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Yes. Imagine that the king is on the lower left square and that on each move he takes a step along the main diagonal toward the upper right. After his first move and Black’s response, there must be no rooks on the lowest three ranks or the leftmost three files, or the king could immediately reach a threatened square. After his 998th move, the king arrives at a similar situation in the upper right: At this point there must be no rooks on the uppermost three ranks or the rightmost three files, for the same reason. This means that when the king begins his journey, all the rooks must be northeast of him, and when he finishes, all must be southwest. During the trip, then, each of Black’s 499 rooks must change both its rank and its file, in order to keep out of his way. This requires 499 x 2 = 998 moves. So, at the latest, Black will run out of time just a half-move too soon: White will squeeze Black’s maneuvering room down to zero on his own 998th move, just before Black evacuates the last rook. From Miodrag Petkovic, Mathematics and Chess, 1997.

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March 26, 2014April 6, 2014 | Puzzles

Black and White

agnel chess problem

By Hyacinth R. Agnel. White to mate in two moves.

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1. Qc7! cxd2 2. Qc3# From American Chess-Nuts, 1868.

March 21, 2014March 30, 2014 | Puzzles

Black and White

shinkman chess problem

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

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If White could pass his turn, Black would have to promote the pawn or play 1. … Kd1, inviting mate in every variation: 2. Kd1 Qxd2# 2. d1=Q(or R) Bh4# 2. d1=B (or N) Bd2# To reach these lines, White needs to play a waiting move now. But this is tricky to find: If he marks time by moving the bishop, then Black can mark time by advancing the g-pawn. And if White moves the king to b3, b2, b1, or a1, then Black can promote the pawn with check. The only safe move is 1. Ka3!, and now Black must submit to one of the lines above. From the St. John Globe, 1905.

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March 14, 2014March 23, 2014 | Puzzles