Statistics

Adding Probabilities When Events Are Independent

Students add P(A)P(A) and P(B)P(B) to find the chance that two independent events both happen.

Quick check

Why students make it

Students often connect the word independent with separate chances, so they treat the events as a list to add. They mix up the rule for "A or B" with the rule for "A and B."

The rule done right

For independent events that both happen, multiply the probabilities. Use P(A∩B)=P(A)⋅P(B)P(A \cap B)=P(A) \cdot P(B).

Related resources

probabilityindependent-eventsmultiplication-rule