Question: In a forum an important question is asked. Persons who formulate an answer give the correct answer with a 71% probability. How many people have to answer at least to the question, so you at least get a correct answer with a probability of at least 92%?
Properties of the Binomial
Expected value μ = E(X) = n*p
Variance σ² = Var(X) = n*p*q = n*p*(1-p)
Properties of the Hypergeometric distribution
Expected value μ = E(X) =
Variance σ² = Var(X) =
Two quantities
|A ∪ B| = |A| + |B| - |A ∩ B|
Three quantities
|A ∪ B ∪ C| = |A| + |B| + |C| - |A ∩ B| - |A ∩ C| - |B ∩ C| + |A ∩ B ∩ C|