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Probability

Probability​

Core formulas:

Probability = favorable outcomes / total outcomes
P(not A) = 1 - P(A)
P(A or B) = P(A) + P(B) - P(A and B)

Independent events:

P(A and B) = P(A) * P(B)

Conditional probability:

P(A given B) = P(A and B) / P(B)

At least one:

P(at least one success) = 1 - P(no success)

Binomial probability:

For n trials, success probability p:
P(exactly r successes) = nCr * p^r * (1-p)^(n-r)

Common traps:

  • Without replacement changes probability after each draw.
  • With replacement keeps probability constant.
  • Probability is never below 0 or above 1.