Probability
The likelihood that a certain event will occur. The formula is: probability = (number of desired or successful outcomes) / (total number of possible outcomes). The probability that some event definitely will occur is 1, or 100%. The probability that some event definitely will not occur is 0, or 0%. Further, the collection of all possible outcomes of a particular scenario add up to a probability of 1, or 100%.
“And” in probability
To determine the probability that event A and event B will both occur, find the individual probabilities of each event and multiply them together. “and” = “multiply”.
“Or” in probability
To determine the probability that event A or event B will occur (and assuming that event A and event B cannot both happen together), find the individual probabilities of each event and add them together. “or” = “add” .
Note:
If event A and event B could both occur together, then to calculate the probability that either event A or event B occurs, find the individual probabilities of each event, add them together, and then subtract the probability that the two events will happen together.
