Key Takeaways
- Kolmogorov's first axiom states that the probability of any event is a non-negative real number, ensuring P(E) ≥ 0 for all events E in the sample space.
- Kolmogorov's second axiom requires that the probability of the entire sample space is exactly 1, i.e., P(Ω) = 1, normalizing all probabilities.
- Kolmogorov's third axiom specifies that for any countable collection of mutually exclusive events, the probability of their union equals the sum of their individual probabilities.
- The binomial distribution Bin(n,p) gives the probability of exactly k successes in n independent Bernoulli trials: P(K=k) = C(n,k) p^k (1-p)^{n-k}.
- For Bin(10,0.5), the mode is 5 with P(K=5) ≈ 0.2461, highest probability mass at the mean.
- The expected value of Bin(n,p) is np, linear in trials, e.g., for n=100, p=0.3, E[X]=30.
- The normal distribution N(μ,σ²) has density φ(x) = (1/(σ√(2π))) exp(-(x-μ)^2/(2σ²)).
- Standard normal Z~N(0,1) has P(Z ≤ 1.96) ≈ 0.975, used for 95% confidence intervals.
- 68-95-99.7 rule: ≈68% within 1σ, 95% within 2σ, 99.7% within 3σ of mean for normal.
- Central Limit Theorem (CLT) states that sum of i.i.d. with finite variance, normalized, converges to N(0,1).
- Lindeberg-Lévy CLT requires i.i.d. mean μ, var σ²>0, S_n* = (S_n - nμ)/(σ√n) → N(0,1).
- Berry-Esseen theorem bounds CLT approximation error by |F_n(x) - Φ(x)| ≤ C ρ / (σ^3 √n), C≈0.5.
- Birthday problem: P(at least one shared birthday in 23 people) ≈ 0.5073 for 365 days.
- Monty Hall problem: switching doors gives 2/3 probability of winning car.
- In 52-card deck, P(royal flush in 5 cards) = 4 / 2,598,960 ≈ 0.000154%.
This blog post explores probability foundations, key distributions, theorems, and surprising real-world applications.
Advanced Theorems
Advanced Theorems Interpretation
Applications and Examples
Applications and Examples Interpretation
Continuous Distributions
Continuous Distributions Interpretation
Discrete Distributions
Discrete Distributions Interpretation
Foundational Concepts
Foundational Concepts Interpretation
Sources & References
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- Reference 13SOCIETYOFACTUARIESsocietyofactuaries.orgVisit source






