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From Algorithms to Z-Scores - matloff - University of California, Davis

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ii CONTENTS<br />

2.12.5 Back <strong>to</strong> the Board Game Example . . . . . . . . . . . . . . . . . . . . . . . . 25<br />

2.12.6 How Long Should We Run the Simulation? . . . . . . . . . . . . . . . . . . . 25<br />

2.13 Combina<strong>to</strong>rics-Based Probability Computation . . . . . . . . . . . . . . . . . . . . . 26<br />

2.13.1 Which Is More Likely in Five Cards, One King or Two Hearts? . . . . . . . . 26<br />

2.13.2 Example: Lottery Tickets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27<br />

2.13.3 “Association Rules” in Data Mining . . . . . . . . . . . . . . . . . . . . . . . 28<br />

2.13.4 Multinomial Coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 29<br />

2.13.5 Example: Probability <strong>of</strong> Getting Four Aces in a Bridge Hand . . . . . . . . . 30<br />

3 Discrete Random Variables 35<br />

3.1 Random Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35<br />

3.2 Discrete Random Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35<br />

3.3 Independent Random Variables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36<br />

3.4 Expected Value . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36<br />

3.4.1 Generality—Not Just for DiscreteRandom Variables . . . . . . . . . . . . . . 36<br />

3.4.1.1 What Is It? . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br />

3.4.2 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37<br />

3.4.3 Computation and Properties <strong>of</strong> Expected Value . . . . . . . . . . . . . . . . . 37<br />

3.4.4 “Mailing Tubes” . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42<br />

3.4.5 Casinos, Insurance Companies and “Sum Users,” Compared <strong>to</strong> Others . . . . 43<br />

3.5 Variance . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br />

3.5.1 Definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44<br />

3.5.2 Central Importance <strong>of</strong> the Concept <strong>of</strong> Variance . . . . . . . . . . . . . . . . . 47<br />

3.5.3 Intuition Regarding the Size <strong>of</strong> Var(X) . . . . . . . . . . . . . . . . . . . . . . 47<br />

3.5.3.1 Chebychev’s Inequality . . . . . . . . . . . . . . . . . . . . . . . . . 48<br />

3.5.3.2 The Coefficient <strong>of</strong> Variation . . . . . . . . . . . . . . . . . . . . . . . 48<br />

3.6 Indica<strong>to</strong>r Random Variables, and Their Means and Variances . . . . . . . . . . . . . 48

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