Formules

Calculatrice de probabilité

Calculez une probabilité à partir des issues favorables et du total, ou combinez deux événements indépendants (A et B, A ou B, aucun, exactement un).

Les issues que vous voulez, ex. 3 boules rouges
Toutes les issues équiprobables

Résultat

Saisissez les valeurs et appuyez sur Calculer pour voir le résultat.

Formule

P(E)=favourable outcomestotal outcomesP(E) = \frac{\text{favourable outcomes}}{\text{total outcomes}}

For equally likely outcomes.

P(not E)=1−P(E)P(\text{not } E) = 1 - P(E)

The complement: the event does not happen.

P(A∩B)=P(A) P(B)P(A \cap B) = P(A)\,P(B)

Both happen, when A and B are independent.

P(A∪B)=P(A)+P(B)−P(A∩B)P(A \cup B) = P(A) + P(B) - P(A \cap B)

At least one happens.

Comment utiliser cette calculatrice

  1. For one event, enter how many outcomes you want and how many there are in total.
  2. For two independent events, enter each probability as a fraction (1/2) or a decimal (0.5).

Exemple corrigé

3 red balls in a bag of 8

P(red) = 3/8 = 0.375 = 37.5%.

P(not red) = 1 − 3/8 = 5/8.

The odds of red are 3 : 5 (3 for, 5 against).

Questions fréquentes

What does independent mean?

One event does not change the chance of the other — like two separate coin flips.

What is the difference between probability and odds?

Probability compares favourable outcomes with all outcomes (3/8); odds compare favourable with unfavourable (3 : 5).