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• December 2020: Maximal losing vote

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• November 2020: The power game

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• October 2020: Control-flow graphs

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• September 2020: Generalized Rock Paper Scissors

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• August 2020: Tweaking the "Nim" game

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• July 2020: Sequences generated by letters

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• June 2020: Farewell and welcome to Gadi Aleksandrowicz!

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• May 2020: Conway's Game of Life

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• April 2020: COVID-19 outbreak

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• March 2020: Dic-dac-doe

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• February 2020: Snakes and Ladders

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• January 2020: 2 poisonous barrels

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• December 2019: Approximating absolute value

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• November 2019: Large 9x9 determinant

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• October 2019: Five banknotes II

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• September 2019: Five banknote denominations

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• August 2019: Three restricted permutations cannot cover

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• July 2019: Large- and small-area knight's cycles

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• June 2019: Two close sums of the square root of smooth numbers

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• May 2019: Longest boat trip

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• April 2019: Prime magic square

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• March 2019: Rational approximation of square root

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• February 2019: Debater's score

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• January 2019: Charlie helps Bob defeat Alice

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• December 2018: Two circles multiplication create a square

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• November 2018: 10-choose-5 short string

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• October 2018: Different area triangles

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• September 2018: Mono-gender in three-letter words

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• August 2018: (Almost) prime water sharing

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• July 2018: Aging obscure triplets

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• June 2018: Five L/J Tetrominoes

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• May 2018: Two fake coins

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• April 2018: 9 Balloons

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• March 2018: Alice and Bob and Six Switches

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• February 2018: 3 people throw dice

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• January 2018: Fake news spread

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• December 2017: Quad9 six degrees of separation

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• November 2017: A die and two coins

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• October 2017: IBM security polynomial

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• September 2017: Fischer’s Fool’s Mate

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• August 2017: Billiard

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• July 2017: Zeros in sin(PONDER)*sin(THIS)

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• June 2017: Math exercise to 100

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• May 2017: Letter gaps

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• April 2017: Factoring

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• March 2017: Eight octopuses with watches

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• February 2017: How many Boolean sequences

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• January 2017: Rational solutions for x**y=y**x

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• December 2016: Fair rope pulling

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• November 2016: Game of 12 months chefs

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• October 2016: The best five-digit number

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• September 2016: Seating four people for 24 hours

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• August 2016: Finding bags of counterfeit coins

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• July 2016: Pentominos tiling (Golomb)

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• June 2016: Tilting a truncated icosahedron

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• May 2016: Attacking chess pieces

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• April 2016: RoboCats falling by cubic polynomial

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• March 2016: Squareversed numbers

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• February 2016: IBM InterConnect

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• January 2016: Efficient bicycle gears

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• December 2015: EBCDIC to ASCII conversion

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• November 2015: Watson verbal arithmetic

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• October 2015: Counting 12 bits using 5-to-2 functions

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• September 2015: Awarding N people with 8 multi-person teams

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• August 2015: Loopsless projections of a loop

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• July 2015: Four people with 1-6 hats

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• June 2015: Drifting complex anomaly detection

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• May 2015: 3 people betting game

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• April 2015: 7x7x7 with as much Peters

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• March 2015: Punched (twice) tape

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• February 2015: Kakuro - hard version

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• January 2015: Kakuro - easy version

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• December 2014: A matrix with 29 solutions

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• November 2014: Distribution using two coins

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• October 2014: Last digits of 2^3^4^5^6^7^8^9

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• September 2014: 2^3^4^5 leading digit on base e

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• August 2014: Biased binary search

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• July 2014: Pebbles game on a tetrahedron

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• June 2014: 25 intersecting Cubes

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• May 2014: Annihilation probability of 1D gun

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• April 2014: 1D version of the 2048 game

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• March 2014: Toggling lamps

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• February 2014: Juxtaposing a 4D pyramids

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• January 2014: Boolean 21x6 matrix

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• December 2013: Gifts graph

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• November 2013: K-dim faces of d-dim hypercube

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• October 2013: B&W coloring of a chess board

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• September 2013: Bob and Alice vs the casino

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• August 2013: Letters on a 9D hypercube

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• July 2013: Octahedronial dice

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• June 2013: Find a fraction

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• May 2013: Computing a polynomial

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• April 2013: Sum of fractions

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• March 2013: Buying 5 products

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• February 2013: Concatenating squares

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• January 2013: 13 permutation on 18 letters

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• December 2012: Maximal sum 6x6 grid

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• November 2012: Lattice of trees blocks light

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• October 2012: Disdyakis Triacontahedrons dice

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• September 2012: Parking game

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• August 2012: 3 charges that almost cancel out

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• July 2012: Coloring balls games

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• June 2012: Dividing 1,506,009,006,001,500,000,000

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• May 2012: Permutation scheduling

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• April 2012: Garden hose model

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• March 2012: Balanced binary tree

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• February 2012: Biased coin game

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• January 2012: Exploding dragon egg

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• December 2011: Infinite chess game

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• November 2011: Volleyball tournament

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• October 2011: Interesting resistors network

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• September 2011: Bits to dice and back

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• August 2011: Triangle area / perimeter

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• July 2011: School lunches

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• June 2011: Parking density

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• May 2011: Distance between bad bars

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• April 2011: How many snakes

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• March 2011: Locating faulty bits

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• February 2011: Flippable number

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• January 2011: Letters and beans game

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• December 2010: Counting votes from percentage

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• November 2010: In honor of Benoit Mandelbrot

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• October 2010: Finding the size of a pentagon

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• September 2010: Threaded robot looks for a line

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• August 2010: Lilliput unique ID numbers

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• July 2010: 1,000,000,000 divides round((1+2cos(20))**n)

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• June 2010: A bug in a Boolean circuit

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• May 2010: Quantization of probability vector

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• April 2010: Hex = dec, removing last 21 digits

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• March 2010: Spell names by passing phones

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• February 2010: 5 moves chess game

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• January 2010: Make a 5 from 2 and 2

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• December 2009: Finding 25 bits number using masks

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• November 2009: Fastest way to find the smallest divisor

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• October 2009: Complete the sequence

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• September 2009: Non repeating cumulative sum

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• August 2009: Implement 3 nots using only 2

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• July 2009: Ending a backgammon game with a double

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• June 2009: Value of expression regarding permutation

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• May 2009: Palindrome time

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• April 2009: 5-ops implementation of erasure code

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• March 2009: Hexadecimal exercise

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• February 2009: Find a bug in this unknown riddle

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• January 2009: Value of a replaceable lottery ticket

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• December 2008: Probability of random walk tetrominoes

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• November 2008: Ponder^this = ponder...

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• October 2008: Jumping frog

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• September 2008: Partitioning 13x13 to squares

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• August 2008: Variation on the 8-queen problem

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• July 2008: Covering pentominoes by polyominos

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• June 2008: Probability of DNA testing

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• May 2008: Game of life - backwards

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• April 2008: Polygons formed from squares / triangles

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• March 2008: How much to bid?

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• February 2008: What are the rules of the game?

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• January 2008: Buying random balls out of an urn

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• December 2007: Finding intermittently failing parts

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• November 2007: Revealing sets of lights

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• October 2007: Resistance of Platonic solids

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• September 2007: Bundle deal of cable TV

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• August 2007: Describe the sequence

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• July 2007: Minimum length of blocking fence

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• June 2007: Sum of random (0,1) game

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• May 2007: Largest square in a cube

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• April 2007: Random walk of a frog

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• March 2007: Shooter / target game

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• February 2007: When to discard a random number?

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• January 2007: Future contracts - how many to buy?

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• December 2006: Cycles size in random permutation

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• November 2006: Expressions with 1,2,3,4

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• October 2006: Fraction of area of triangle

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• September 2006: f(n)=(1+(n*n-n)*f(n-1))/(n*n+1)

  Challenge | Solution

• August 2006: Value of future contract

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• July 2006: Approximations of 1/x and sqrt(x)

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• June 2006: Fraction of vertical dominoes

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• May 2006: Distance configuration of 4 points

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• April 2006: Random walk on a hypercube

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• March 2006: Expected area of random triangle

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• February 2006: Random [0,1] poker game

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• January 2006: Size of smallest/largest piece

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• December 2005: Barring polyominoes from infinite board

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• November 2005: Size of finite random binary tree

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• October 2005: Matrices with special 2x2 minors

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• September 2005: Acceleration rate of pulley system

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• August 2005: first N digits of M is divisible by N

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• July 2005: Covering table with coins

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• June 2005: Almost balanced A/B strings

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• May 2005: Rectangular grid / glass cubes

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• April 2005: Divisibility of integer powers

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• March 2005: 6x6x6 cube with different signatures

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• February 2005: Infinite right triangles

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• January 2005: 7-colored 35 beads necklace

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• December 2004: Projecting points onto the complex plane

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• November 2004: Sum of numbers after worm ate some

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• October 2004: GCD of values of primitive polynomial

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• September 2004: Another versions of turntable

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• August 2004: Longest way to come home

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• July 2004: N cups on a turntable

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• June 2004: Rectangles in the unit square

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• May 2004: A twist on "Towers of Hanoi" puzzle

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• April 2004: Labeling VCR cassettes using digit stickers

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• March 2004: Number of weakly monotone arrays

  Challenge | Solution

• February 2004: Right isosceles triangle with integer sides

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• January 2004: Finding duplicates in read-only array

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• December 2003: Similar dissection of quadrilaterals

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• November 2003: Line intersecting curve in a pentagon

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• October 2003: Non attacking new chess pieces II

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• September 2003: Irrational root of polynomial

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• August 2003: Non attacking chess pieces

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• July 2003: Coloring roads to enable blind direction

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• June 2003: Partitioning a square into rectangles

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• May 2003: sqrt(1+2*sqrt(1+3*sqrt(...+n*sqrt(1]

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• April 2003: Bounds on a Hamiltonian tour

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• March 2003: Fencing a pasture

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• February 2003: Zero sum in Boolean cards

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• January 2003: 4 points with odd integer distances

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• December 2002: 4 integers with squares sums

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• November 2002: 4 bottles on a square turntable

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• October 2002: Tournament of N with <=M players

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• September 2002: Closed subsets of boolean operators

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• August 2002: Drawing 4D hypercube on a grid

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• July 2002: 23 prisoners and a switch room

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• June 2002: Coin weighing using scale

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• May 2002: Circle passing via 7 lattice points

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• April 2002: Lifetime of adjacent differences

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• March 2002: Coffe or tea majority club

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• February 2002: Undirected graph of diameter 2

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• January 2002: Gambling casino

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• December 2001: Knight's tour on 4xN chess boards

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• November 2001: PB&J asymmetry bounds

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• October 2001: f maps any open interval onto R

  Challenge | Solution

• September 2001: Bounds on a permutation group

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• August 2001: Points on a plane

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• July 2001: 1/1 + 2/(2+3) + 3/(4+5+6) + ...

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• June 2001: Goblin chase in a train

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• May 2001: Goblin chase in a pool

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• April 2001: College saving account

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• March 2001: Golf - hit in one

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• February 2001: Kubricia's 2001 money boxes

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• January 2001: Counting segments overlays

  Challenge | Solution

• December 2000: Commuter gets 20 minutes earlier

  Challenge | Solution

• November 2000: 75 integers in [1,230]

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• October 2000: One+five(four) cards trick

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• September 2000: Simplify sqrt expression

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• August 2000: Six Card Cribbage

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• July 2000: 2-dimensional grid jumping coins

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• June 2000: Coins game (6.78$)

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• May 2000: Northwest to the north pole

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• April 2000: Revamp the tax code

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• March 2000: Sum of two squares

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• February 2000: N**C is integer

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• January 2000: Catching baseball

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• December 1999: Zero-less multiply of 2**1999

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• November 1999: Cutting a cube into a box

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• October 1999: Path 1 or 2 in directed graph

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• September 1999: Recognizing dishes

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• August 1999: Seating people on N+M tables

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• July 1999: Labeling bowling pins

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• June 1999: 1 plus 1/7 of the medals

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• May 1999: Integer side rectangles partition

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• April 1999: Wally's Rock Permuting (WRP)

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• March 1999: Cliques of people in a ballroom

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• February 1999: A leashed sheep eats grass

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• January 1999: Water glass center of mass

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• December 1998: Removing snow

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• November 1998: Cutting frosted cake

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• October 1998: Sorting pancakes

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• September 1998: Magic Star of David

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• August 1998: Equilateral triangle

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• July 1998: Tennis balls in a bucket

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• June 1998: Shaking hands in a party

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• May 1998: A belt around the earth

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