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- Introduction to Probability
Probability
Introduction to Probability
A first course in probability, from events, counting and conditional probability to random variables, discrete and continuous distributions, limit theorems, simulation and Markov chains.
- Introductory
- 84 lessons
- Free
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About this course
Probability is the mathematics of uncertainty. A probability model describes what can happen and assigns probabilities that obey a few rules, and those rules underlie statistics, simulation and the analysis of risk. This course starts from events and the probability axioms and works through counting, conditional probability and Bayes’ theorem, discrete random variables and their standard distributions, joint distributions, conditional expectation and a law of large numbers for averages. It then introduces the calculus needed for continuous distributions and continues with the exponential and normal models, the central limit theorem, simulation, random walks, Poisson processes and small Markov chains.
The videos are coming out one at a time, in course order. Every lesson has its own page with precise definitions, a worked example for each key term and a few exercises with answers, so you can start reading now.
The reference sheet collects the definitions, rules, distributions and theorems unit by unit, with the conditions each one needs and links to the lessons that explain them.
No calculus is needed to start. Fractions, percentages and elementary algebra are enough for the early lessons, and before continuous distributions the course teaches the basic integrals and derivatives they need, as a short bridge rather than a full calculus course. A few later lessons also rely on the exponential function and on matrix multiplication. In Precalculus, the Exponential and Logarithmic Functions unit covers the functions behind the Poisson and exponential distributions, and the Systems, Vectors, and Matrices unit covers matrix multiplication. Calculus develops integrals and derivatives fully, including a lesson on integration in probability theory.
Statistics teaches the probability it needs on its own, so the two courses can be taken in either order. Its lessons on sampling distributions, standard errors, confidence intervals, tests and Bayesian updating use ideas developed here, and the lesson pages of this course point to them. Multivariate Statistical Analysis lists probability and random variables among its prerequisites, and the joint distributions, covariance and correlation from this course return there as random vectors and covariance matrices.
Good to know first
- Fractions and percentages
- Elementary algebra
- Reading graphs and tables
Course outline
1 of 84 lessons are on YouTube so far. Each lesson is one video. Open a unit to see its lessons, or follow a lesson for its definitions and examples.
Probability Foundations
1 of 8 lessons on YouTubeOpen the Probability Foundations unit pageProbability Models and Events
- Probability Models and UncertaintyOn YouTube
Video 1
experiment, trial, outcome, event, probability model, theoretical probability, empirical relative frequency and subjective probability
Also uses fractions and percentages, elementary algebra and reading tables and graphs.
- Sample Spaces and EventsComing soon
Video 2
sample space, union, intersection, complement, set difference, De Morgan’s laws, disjoint events and partition
Builds on Probability Models and Uncertainty.
- Translating Event LanguageComing soon
Video 3
inclusive or, neither, not both, exactly one, at least, at most, only if and counterexample
Builds on Sample Spaces and Events.
The Axioms and Basic Rules
- Probability Axioms and Basic RulesComing soon
Video 4
probability axioms, nonnegativity, normalization, countable additivity, pairwise disjoint events, probability of the empty event and monotonicity
Builds on Sample Spaces and Events.
- The Complement RuleComing soon
Video 5
complement rule, complementary partition, at least one, not all and complement of at least k
Builds on Probability Axioms and Basic Rules and Translating Event Language.
- The Addition RuleComing soon
Video 6
addition rule, overlap, disjoint regions, exactly one of two events and union bound
Builds on Probability Axioms and Basic Rules and Translating Event Language.
Equally Likely Outcomes and Simulation
- Equally Likely OutcomesComing soon
Video 7
equally likely outcomes, uniform finite model, favorable outcomes, cardinality, level of detail and ordered sequences
Builds on Probability Axioms and Basic Rules, The Complement Rule and The Addition Rule.
- Probability SimulationComing soon
Video 8
simulation, simulated trial, pseudorandom generator, random seed, reproducibility, running estimate and sampling variability
Builds on Equally Likely Outcomes.
Counting and Equally Likely Models
7 lessons coming soonOpen the Counting and Equally Likely Models unit pageOrdered and Unordered Selections
- Sum and Product Rules for CountingComing soon
Video 9
product rule for counting, sum rule for counting, counting by cases, selection with replacement, selection without replacement, counting with restrictions and decision tree
Builds on Equally Likely Outcomes.
- PermutationsComing soon
Video 10
factorial, zero factorial, permutation, partial permutation and circular arrangement
Builds on Sum and Product Rules for Counting.
- Combinations and Binomial CoefficientsComing soon
Video 11
combination, binomial coefficient, overcounting, symmetry of binomial coefficients, Pascal’s identity, Pascal’s triangle and binomial theorem
Builds on Permutations.
- Repeated Objects and Multinomial CountingComing soon
Video 12
multiset permutation, indistinguishable objects, multinomial coefficient, counting by choosing positions, allocation to named groups and multinomial expansion
Builds on Combinations and Binomial Coefficients.
Overlaps and Collisions
- Inclusion-ExclusionComing soon
Video 13
inclusion-exclusion principle, pairwise intersection, triple intersection, disjoint Venn regions, exactly one of three events and exactly two of three events
Builds on The Addition Rule and Combinations and Binomial Coefficients.
- Birthday and Collision ProblemsComing soon
Video 14
collision, no-collision probability, birthday problem, match of a specified pair, pigeonhole principle and nonuniform categories
Builds on Inclusion-Exclusion and The Complement Rule.
Choosing a Counting Method
- Choosing a Counting MethodComing soon
Video 15
ordered selection, unordered selection, unordered selection with repetition, multiplicity of a record, equal likelihood after erasing order and counting by complement
Builds on Sum and Product Rules for Counting, Permutations, Combinations and Binomial Coefficients, Repeated Objects and Multinomial Counting, Inclusion-Exclusion and Birthday and Collision Problems.
Conditioning, Independence and Evidence
9 lessons coming soonOpen the Conditioning, Independence and Evidence unit pageConditional Probability
- Conditional ProbabilityComing soon
Video 16
conditional probability, conditioning event, reference group, reversed condition and positive-probability requirement
Builds on Probability Axioms and Basic Rules and The Addition Rule.
- Conditional Probability TablesComing soon
Video 17
two-way table, joint probability, marginal probability, margins, row and column percentages and natural frequencies
Builds on Conditional Probability.
Independence
- Independent EventsComing soon
Video 18
independent events, product criterion, dependent events, independence of complements, pairwise independence and mutual independence
Builds on Conditional Probability.
- Disjoint Events and IndependenceComing soon
Video 19
disjoint events with positive probability, overlapping independent events, overlapping dependent events, zero-probability event and nested events
Builds on Independent Events and The Addition Rule.
Trees, Total Probability and Bayes’ Theorem
- Probability Trees and the Chain RuleComing soon
Video 20
probability tree, conditional branch, multiplication rule, chain rule, terminal path and branch normalization
Builds on Sum and Product Rules for Counting, Conditional Probability and Independent Events.
- The Law of Total ProbabilityComing soon
Video 21
law of total probability, group weight, conditional rate, weighted average and zero-weight group
Builds on Conditional Probability and Probability Trees and the Chain Rule.
- Bayes’ Theorem and Base RatesComing soon
Video 22
Bayes’ theorem, prior probability, likelihood, posterior probability, base rate neglect, sensitivity, specificity and false positive rate
Builds on The Law of Total Probability.
Combining Evidence
Video 23
conditional independence, latent state, shared cause, marginal dependence, sequential updating and duplicated evidence
Builds on Bayes’ Theorem and Base Rates and Independent Events.
- Probability and OddsComing soon
Video 24
odds in favor, odds against, probability from odds, likelihood ratio, prior odds, posterior odds and odds form of Bayes’ theorem
Builds on Bayes’ Theorem and Base Rates and Conditional Independence and Sequential Evidence.
Discrete Random Variables and Expected Value
6 lessons coming soonOpen the Discrete Random Variables and Expected Value unit pageRandom Variables and Their Distributions
- Discrete Random VariablesComing soon
Video 25
random variable, realization, discrete random variable, support, countably infinite support and distribution of a random variable
Builds on Equally Likely Outcomes, Conditional Probability and Independent Events.
- Probability Mass FunctionsComing soon
Video 26
probability mass function, nonnegative masses, normalizing constant, event probability as a sum of masses, finite uniform distribution and probability bar chart
Builds on Discrete Random Variables.
- Cumulative Distribution FunctionsComing soon
Video 27
cumulative distribution function, step function, jump size, right-continuity, tail probability and interval probability
Builds on Probability Mass Functions.
- Functions of Discrete Random VariablesComing soon
Video 28
function of a random variable, preimage, one-to-one map, many-to-one map, collecting probability mass and positive part
Builds on Probability Mass Functions and Cumulative Distribution Functions.
Expected Value
- Expected ValueComing soon
Video 29
expected value, probability-weighted average, mode, conditional mean, net gain, infinite expectation and absolute integrability
Builds on Discrete Random Variables and Probability Mass Functions.
- Expected Value and DecisionsComing soon
Video 30
expected payoff, net payoff, fair price, break-even probability, expected cost, model risk and decision criterion
Builds on Expected Value.
Expectation, Spread, Sums and Averages
6 lessons coming soonOpen the Expectation, Spread, Sums and Averages unit pageLinearity and Indicators
- Linearity of ExpectationComing soon
Video 31
linearity of expectation, expectation of a sum, linear combination, expectation of a product, expectation of a square and finite expectation
Builds on Expected Value and Functions of Discrete Random Variables.
- Indicator Random VariablesComing soon
Video 32
indicator random variable, expectation of an indicator, sum of indicators, expected count, indicator of a union and expected number of distinct categories
Builds on Linearity of Expectation and Discrete Random Variables.
Variance and Standard Deviation
- VarianceComing soon
Video 33
variance, deviation from the mean, squared deviation, second moment, computational formula for variance, squared units and finite second moment
Builds on Expected Value, Linearity of Expectation and Functions of Discrete Random Variables.
- Standard Deviation and Changing ScaleComing soon
Video 34
standard deviation, root-mean-square deviation, mean absolute deviation, shift, change of scale, affine transformation and change of units
Builds on Variance.
Sums and Sample Means
- Sums of Discrete Random VariablesComing soon
Video 35
distribution of a sum, ordered-pair table, discrete convolution, variance of an independent sum and cross term
Builds on Independent Events, Probability Mass Functions, Linearity of Expectation and Variance.
- Sample Means and Sampling DistributionsComing soon
Video 36
random sample, sample mean, statistic, sampling distribution, independent and identically distributed and standard error
Builds on Sums of Discrete Random Variables and Cumulative Distribution Functions.
Discrete Probability Distributions
7 lessons coming soonOpen the Discrete Probability Distributions unit pageUniform and Bernoulli Distributions
- The Discrete Uniform DistributionComing soon
Video 37
discrete uniform distribution, number of support values, mean by symmetry, variance of consecutive integers, sum-of-squares identity and evenly spaced support
Builds on Probability Mass Functions, Expected Value and Variance. Also uses the sum of the first n positive integers.
- The Bernoulli DistributionComing soon
Video 38
Bernoulli distribution, Bernoulli trial, success, parameter of a distribution, mean and variance of a Bernoulli variable, degenerate distribution and maximum Bernoulli variance
Builds on Probability Mass Functions, Expected Value and Variance.
Counting and Waiting in Independent Trials
- The Binomial DistributionComing soon
Video 39
binomial distribution, binomial probability formula, binomial assumptions, mean of a binomial count, variance of a binomial count and binomial tail probability
Builds on The Bernoulli Distribution, Combinations and Binomial Coefficients, Variance, Sums of Discrete Random Variables and Indicator Random Variables.
- The Geometric DistributionComing soon
Video 40
geometric distribution, trial-count convention, failure-count convention, geometric series, geometric tail, memoryless property and mean and variance of a geometric distribution
Builds on The Bernoulli Distribution and The Binomial Distribution.
- The Negative Binomial DistributionComing soon
Video 41
negative binomial distribution, stopping rule, waiting time for the rth success, failure-count form, sum of geometric waiting times and deadline probability as a binomial tail
Builds on The Geometric Distribution, The Binomial Distribution and Combinations and Binomial Coefficients.
Finite Populations and Poisson Counts
- Hypergeometric DistributionsComing soon
Video 42
hypergeometric distribution, finite population, sampling without replacement, support of a hypergeometric count, finite population correction and dependent draws
Builds on Combinations and Binomial Coefficients, Probability Trees and the Chain Rule and The Binomial Distribution.
- Poisson DistributionsComing soon
Video 43
Poisson distribution, Poisson parameter, rate times exposure, exponential series, Poisson mean and variance and Poisson approximation to the binomial
Builds on The Binomial Distribution, Expected Value and Variance. Also uses the exponential function and the number e.
Joint Discrete Laws and Conditional Averages
8 lessons coming soonOpen the Joint Discrete Laws and Conditional Averages unit pageJoint, Marginal and Conditional Distributions
- Joint Probability Mass FunctionsComing soon
Video 44
random vector, joint probability mass function, joint probability table, joint support, event region and function of a random pair
Builds on Probability Mass Functions and Conditional Probability.
- Marginal Probability DistributionsComing soon
Video 45
marginal distribution, marginal probability mass function, summing out a variable and information lost by marginalizing
Builds on Joint Probability Mass Functions.
- Conditional Probability Mass FunctionsComing soon
Video 46
conditional probability mass function, renormalizing a row or column, reversed conditioning, conditional mean from a conditional PMF and joint probability from conditional and marginal
Builds on Marginal Probability Distributions, Conditional Probability and Expected Value.
Independence and Covariance
- Independent Random VariablesComing soon
Video 47
independent random variables, product law, joint cumulative distribution function, CDF factorization, functions of independent variables and mutual independence of random variables
Builds on Independent Events, Joint Probability Mass Functions, Marginal Probability Distributions, Conditional Probability Mass Functions and Cumulative Distribution Functions.
- Covariance, Correlation and SumsComing soon
Video 48
covariance, correlation coefficient, uncorrelated variables, variance of a sum, bilinearity of covariance, Cauchy-Schwarz inequality and perfect correlation
Builds on Variance, Independent Random Variables and Joint Probability Mass Functions.
Conditional Expectation and Total Variance
- Conditional Expectation and the Tower RuleComing soon
Video 49
conditional expectation, conditional mean function, random conditional mean, law of total expectation, integrability and squared-error prediction
Builds on Expected Value, Linearity of Expectation and Conditional Probability Mass Functions.
- The Law of Total VarianceComing soon
Video 50
conditional variance, law of total variance, within-group variation and between-group variation
Builds on Variance, Covariance, Correlation and Sums and Conditional Expectation and the Tower Rule.
- Random Sums with Independent CountsComing soon
Video 51
random sum, random count, empty sum, mean of a random sum and variance of a random sum
Builds on The Law of Total Variance, Poisson Distributions and Linearity of Expectation.
Repeated Sampling and the Discrete Law of Large Numbers
6 lessons coming soonOpen the Repeated Sampling and the Discrete Law of Large Numbers unit pageAverages and Probability Bounds
- Mean and Variance of the Sample MeanComing soon
Video 52
realized average, unbiasedness, variance of the sample mean, standard error of the mean and square-root scaling
Builds on Sample Means and Sampling Distributions, Independent Random Variables and Covariance, Correlation and Sums.
- Markov and Chebyshev InequalitiesComing soon
Video 53
probability bound, Markov’s inequality, Chebyshev’s inequality, sharp bound, two-sided deviation event and bound in standard deviation units
Builds on Expected Value, Variance and Mean and Variance of the Sample Mean.
The Law of Large Numbers and Streaks
- Law of Large Numbers for Discrete VariablesComing soon
Video 54
weak law of large numbers, convergence in probability, error tolerance, relative frequency, sufficient sample size and finite-sample uncertainty
Builds on Markov and Chebyshev Inequalities, Mean and Variance of the Sample Mean and The Binomial Distribution.
- Streaks and the Gambler’s FallacyComing soon
Video 55
streak, gambler’s fallacy, dilution, compensation misconception, run at a preselected position and learning about an unknown probability
Builds on Law of Large Numbers for Discrete Variables and Independent Events.
Simulation Error
- Simulation Error and Number of TrialsComing soon
Video 56
simulation estimate, Monte Carlo error, plug-in standard error, conservative standard error, replication, model error and implementation error
Builds on Probability Simulation, Mean and Variance of the Sample Mean and Law of Large Numbers for Discrete Variables.
- A Repeated-Sampling InvestigationComing soon
Video 57
repeated sampling, exact benchmark, empirical distribution, empirical variance and replication count
Builds on Simulation Error and Number of Trials, The Binomial Distribution and Law of Large Numbers for Discrete Variables.
Continuous Probability and Its Mathematical Tools
6 lessons coming soonOpen the Continuous Probability and Its Mathematical Tools unit pageIntegrals and Derivatives for Probability
- Integrals and Probability as AreaComing soon
Video 58
probability density, probability as area, Riemann sum, definite integral, limits of integration, accumulated probability and power rule for integrals
Builds on Discrete Random Variables, Expected Value and Variance. Also uses areas of rectangles and triangles and an informal idea of a limit.
- Derivatives and the Density-CDF ConnectionComing soon
Video 59
difference quotient, derivative, tangent slope, power rule for derivatives, fundamental theorem of calculus, antiderivative and density as the derivative of the CDF
Builds on Integrals and Probability as Area and Cumulative Distribution Functions.
Densities and Mixed Distributions
- Probability Densities and CDFsComing soon
Video 60
probability density function, absolutely continuous distribution, normalization of a density, density units, CDF of a continuous variable, interval probability from a CDF and zero probability at a point
Builds on Integrals and Probability as Area and Derivatives and the Density-CDF Connection.
- Point Probabilities and Mixed DistributionsComing soon
Video 61
point mass, mixed distribution, CDF jump, left limit of a CDF, probability-zero event and almost surely
Builds on Probability Densities and CDFs and Cumulative Distribution Functions.
Continuous Moments and Uniform Distributions
- Continuous Expectation and VarianceComing soon
Video 62
expected value of a continuous variable, law of the unconscious statistician, variance of a continuous variable, mean of a mixed distribution, infinite mean and moment existence
Builds on Integrals and Probability as Area, Derivatives and the Density-CDF Connection, Probability Densities and CDFs and Variance. Also uses integrals over an unbounded interval.
- Uniform DistributionsComing soon
Video 63
continuous uniform distribution, quantile, percentile, median, mean and variance of a uniform distribution, conditional uniform distribution and change of units for a density
Builds on Probability Densities and CDFs and Continuous Expectation and Variance.
Exponential and Normal Models
4 lessons coming soonOpen the Exponential and Normal Models unit pageExponential Waiting Times
- Exponential DistributionsComing soon
Video 64
exponential distribution, rate, scale parameter, survival function, memorylessness, natural logarithm and exponential quantile
Builds on The Geometric Distribution, Probability Densities and CDFs, Continuous Expectation and Variance and Uniform Distributions. Also uses derivatives of exponential functions and the product rule.
Normal Distributions
- The Normal DistributionComing soon
Video 65
normal distribution, normal density, standard normal distribution, standardization, 68-95-99.7 rule and normal tail probability
Builds on Probability Densities and CDFs and Continuous Expectation and Variance. Also uses using a standard normal table or calculator.
- Normal Probabilities and QuantilesComing soon
Video 66
z-score, standard normal CDF, symmetry of the standard normal CDF, upper-tail probability, normal quantile, inverse CDF and central probability interval
Builds on The Normal Distribution.
Choosing a Continuous Model
- Choosing a Continuous Probability ModelComing soon
Video 67
distribution family, parameter convention, support of a model, tail behavior and model adequacy
Builds on Uniform Distributions, Exponential Distributions, The Normal Distribution and Normal Probabilities and Quantiles.
Transformations, Approximations and Monte Carlo
6 lessons coming soonOpen the Transformations, Approximations and Monte Carlo unit pageChanging Variables and Sampling
- Transformations and Inverse-CDF SamplingComing soon
Video 68
CDF method, monotone transformation, many-to-one transformation, unbounded density, inverse-CDF sampling and generalized quantile
Builds on Probability Densities and CDFs, Uniform Distributions, Exponential Distributions and Cumulative Distribution Functions.
Limit Theorems for Averages
Video 69
weak law of large numbers for continuous variables, running average, Chebyshev bound for a sample mean, conservative bound and perfectly dependent observations
Builds on Law of Large Numbers for Discrete Variables, Continuous Expectation and Variance and Mean and Variance of the Sample Mean.
- The Central Limit TheoremComing soon
Video 70
central limit theorem, standardized sum, convergence in distribution, normal approximation for an average, finite positive variance and heavy tails
Builds on Exponential Distributions, The Normal Distribution, Mean and Variance of the Sample Mean and The Law of Large Numbers for Continuous Variables.
Exact, Approximate and Simulated Answers
- Poisson and Normal ApproximationsComing soon
Video 71
rare-event regime, normal approximation to the binomial, continuity correction, absolute error, relative error and tail accuracy
Builds on The Binomial Distribution, Poisson Distributions, The Normal Distribution and The Central Limit Theorem.
- Monte Carlo Probability and ExpectationComing soon
Video 72
Monte Carlo method, Monte Carlo estimator, Monte Carlo standard error, probability as an expected indicator, square-root cost of precision and approximate interval for a Monte Carlo estimate
Builds on Probability Simulation, Transformations and Inverse-CDF Sampling, Simulation Error and Number of Trials and The Central Limit Theorem.
Video 73
exact model probability, approximation error, simulation error, uncertain model inputs and error interpretation
Builds on Poisson and Normal Approximations and Monte Carlo Probability and Expectation.
Random Processes and Introductory Markov Chains
9 lessons coming soonOpen the Random Processes and Introductory Markov Chains unit pageBernoulli Processes and Random Walks
- Bernoulli ProcessesComing soon
Video 74
random process, time index, Bernoulli process, cumulative count, first success time, disjoint blocks of trials and count and waiting time events
Builds on The Bernoulli Distribution, The Geometric Distribution and The Binomial Distribution.
- Simple Random WalksComing soon
Video 75
simple random walk, increment, position, drift, variance of a random walk, parity restriction and path probability
Builds on Bernoulli Processes, The Binomial Distribution and Covariance, Correlation and Sums.
Poisson Processes
- Poisson Process BasicsComing soon
Video 76
counting process, homogeneous Poisson process, rate of arrivals, independent increments, stationary increments and overlapping counts
Builds on Poisson Distributions, Exponential Distributions and Bernoulli Processes.
- Arrival Counts and Waiting TimesComing soon
Video 77
first arrival time, exponential waiting time, interarrival time, kth arrival time, count and waiting time connection and memoryless waiting
Builds on Poisson Process Basics and Exponential Distributions.
Markov Chains
- Markov Chains and Transition MatricesComing soon
Video 78
Markov chain, state, Markov property, time-homogeneous chain, transition matrix, row-stochastic convention, initial distribution and one-step update
Builds on Conditional Probability, Conditional Independence and Sequential Evidence and Bernoulli Processes. Also uses matrix multiplication.
- Multi-Step Markov ProbabilitiesComing soon
Video 79
n-step transition probability, matrix power, row vector of state probabilities, Chapman-Kolmogorov relation, endpoint probability and visiting probability
Builds on Markov Chains and Transition Matrices.
- Stationary DistributionsComing soon
Video 80
stationary distribution, balance equations, probability flow, convergence of the state distribution, periodic chain and nonunique stationary distribution
Builds on Multi-Step Markov Probabilities.
Hitting Times and Model Checking
- Hitting Times and AbsorptionComing soon
Video 81
hitting time, hitting probability, absorbing state, first-step analysis, boundary condition, expected time to absorption and infinite hitting time
Builds on Conditional Expectation and the Tower Rule, Markov Chains and Transition Matrices and Stationary Distributions.
- Choosing and Checking Markov ModelsComing soon
Video 82
state definition, Markov assumption, refined state, empirical transition matrix, time step, checking time homogeneity and model limitation
Builds on Stationary Distributions and Hitting Times and Absorption.
Integrated Probability Investigations
2 lessons coming soonOpen the Integrated Probability Investigations unit pageComplete Model Investigations
- A Discrete Probability InvestigationComing soon
Video 83
model specification, joint model from conditional rates, binomial count of alerts, conditional expected work, assumption sensitivity and prediction versus simulated output
Builds on Bayes’ Theorem and Base Rates, The Binomial Distribution, Conditional Expectation and the Tower Rule, Law of Large Numbers for Discrete Variables and Simulation Error and Number of Trials.
Video 84
combined probability model, independence of submodels, fixed batch versus fixed time window, checkpoint availability, sensitivity analysis and simulation check of a submodel
Builds on A Discrete Probability Investigation, Uniform Distributions, Exponential Distributions, The Normal Distribution, Monte Carlo Probability and Expectation, Poisson Process Basics, Arrival Counts and Waiting Times, Stationary Distributions, Hitting Times and Absorption and Choosing and Checking Markov Models.