Probability Calculator

Calculate simple probability, conditional probability, and event combinations.

P(A) = 3/6

0.5

50%

Complement P(A')

0.5

Odds in favour

3:3

Probability Calculator Formula & How It Works

P(A) = Favourable Outcomes / Total Outcomes | P(A|B) = P(A∩B) / P(B)
  • Complement: P(A') = 1 − P(A)
  • AND (independent events): P(A∩B) = P(A) × P(B)
  • OR: P(A∪B) = P(A) + P(B) − P(A∩B)
  • Conditional: P(A|B) = P(A and B) / P(B)

Probability measures likelihood on a scale of 0 to 1 (or 0% to 100%). For simple experiments (dice, cards, coins), count favourable outcomes divided by total possible outcomes. For compound events, use addition rule (OR) and multiplication rule (AND). Conditional probability adjusts for known information about event B.

Probability Calculator FAQs

What is the difference between independent and dependent events?

Independent: outcome of one event doesn't affect the other. P(A∩B) = P(A)×P(B). Example: two coin flips. Dependent: first outcome affects second. P(A∩B) = P(A)×P(B|A). Example: drawing cards without replacement.

What is conditional probability?

P(A|B) = probability of A given B has occurred = P(A and B) / P(B). Example: P(rain tomorrow | cloudy today) adjusts rain probability based on current cloudiness. Bayes' theorem extends conditional probability.

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