Probability and Combinatorics

 

 

 

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1  Expectations

 

1.1  Ratio Populations

4

1.2  Differences Between Normal Samples

11

1.3  Biased and Anti-Biased Variance Estimates

13

1.4  Integrating the Bell Curve

16

1.5  The Expectation of Posterior Beliefs

24

1.6  Independence and Negation

28

1.7  Bernoulli Trials

30

1.8  Two-Dimensional Runs in Bernoulli Trials

32

 

 

2  Partitions

 

2.1  Computing the Partitions of n

37

2.2  Additive and Multiplicative Partitions

40

2.3  Partitions into Consecutive Integers

48

2.4  Partition Transform Cycles

50

2.5  Self-Descriptive Numbers and Auto-Valent Partitions

52

2.6  Partitions into Distinct Parts

54

2.7  Probabilities for Splitting Sets

57

2.8  On Euler’s Pentagonal Theorem

64

 

 

3  Randomness

 

3.1  Random High-Low Searching

74

3.2  Expected Area of Random Polygon In a Circle

78

3.3  Probability of a Random Triangle Being Acute

83

3.4  Choice Without Context?

90

3.5  Random Triangles

92

3.6  Generating Random Numbers In Order

94

3.7  Discrete Circular Distributions

95

3.8  N Points On Sphere all in One Hemisphere

100

3.9  A Random Walk Through π

109

3.10  Hail Encounters

111

 

 

4  Urns

 

4.1  Balls In Bins

115

4.2  Bayesian Marbles

118

4.3  Markov's Marbles

120

4.4  A Barrel of Colors and Null Outcomes

122

4.5  Colored Balls in Urns

125

4.6  Balls In Bins With Limited Capacity

128

4.7  Generalized Birthday Problem (N Items in M Bins)

131

4.8  Botches, Failures, and Successes

132

4.9  On Two Trays

134

 

 

5  Permutations

 

5.1  Cumulative Permutation Sequences

137

5.2  Derangements and Generalizations

138

5.3  Permutation Loops

142

5.4  Permutation Puzzles and Logic Problems

150

5.5  Eulerian Numbers

157

 

 

6  Collections

 

6.1  The Collector's Problem

165

6.2  Collecting k Complete Sets of Coupons

167

6.3  Dice Rolling A Given Sum

173

6.4  Round Robin Ties

177

 

 

7  Meetings

 

7.1  Meeting Probabilities

181

7.2  Meeting Combinations and Interval Graphs

188

7.3  Probability of Intersecting Intervals

195

7.4  Combining Probabilities

204

7.5  Witness Words

211

7.6  Probabilities With Renaming

215

7.7  Boolean Expansion as Linear Interpolation

216

7.8  The Shape of Coincidence

218

 

 

8  Gambling

 

8.1  A Two-Stage Lottery

222

8.2  The Gambler's Ruin

223

8.3  Reaching Ruin In Limited Turns

234

8.4  Never Say Never

240

 

 

9  Deals

 

9.1  At Least One Girl

244

9.2  What’s the Deal?

246

9.3  Two Envelopes

257

9.4  Ordered Envelopes

268

 

 

10  Monotone Functions

 

10.1  Generating the Monotone Boolean Functions

272

10.2  Dedekind’s Problem

274

10.3  Progress on Dedekind's Problem

276

 

 

11  Strings

 

11.1  The Statistics of Counterintelligence

281

11.2  Sequences of Characters in Random Strings

283

11.3  Bit-String Orbits Under Rotate-XOR

291

11.4  The e in Petersburg

303

 

 

12  Arrangements

 

12.1  Regular Polygonal Arrangements

310

12.2  Pythagorean Graphs

313

12.3  Two Proofs for a Five Point Star

317

12.4  Golf Tournaments, Polyhedra, and Latin Squares

319

12.5  The Boxer and the Pigeons

322

12.6  Tables of 1 to N with Equal Columns

323

12.7  Coloring The Edges of an Icosahedron

325

12.8  Uniform Squares

328

12.9  Christmas Ornaments

336

12.10  On 13 Bridges

338

 

 

13  Enumerations

 

13.1  Ringing of the Changes (The Shape of 4!)

345

13.2  Complete Projection Cubes

350

13.3  Polyomino Enumerations

358

13.4  The Determinants of 4x4 Magic Squares

360

13.5  414298141056 Quarto Draws Suffice!

361

 

 

14  Miscellaneous

 

14.1  Infinite Parallel Redundancy

367

14.2  A Conditional Protocol

368

14.3  The Coin in Three Fountains

370

14.4  And Then There Were None

371

14.5  Binary Games

375

14.6  f(f(x))=exp(x) Generates the Multinomials

376

14.7  Mnemonic Coins and Pattern Avoidance

377

14.8  Bernoulli Numbers and Harmonic Series

386

14.9  Two In the Shop

388

14.10  Benford's Law

389

14.11  Optimizing Your Wife

393