What is the formula for calculating joint probability?

The correct formula for calculating joint probability involves multiplying the probabilities of two independent events. When two events, A and B, are independent—the occurrence of one does not affect the occurrence of the other—the joint probability is given by P(ab) = P(a) * P(b). This means that to find the probability of both events happening together, you simply multiply their individual probabilities.

In practical terms, if the probability of event A occurring is known and the probability of event B occurring is also known, then you can determine the likelihood of both A and B occurring at the same time by using this multiplication approach. This is fundamental in understanding how multiple independent events interact within probability theory.

The other formulas provided relate to different concepts in probability. For instance, one formula accounts for the inclusion-exclusion principle used to find the probability of either of two events occurring, while others do not describe joint probability accurately.