The notation used to express the probability of event $B$ is denoted as $P(B)$.

In the field of probability, we utilize specific notations to represent the likelihood of various events occurring. The letter $P$ stands for “probability,” and it is followed by the event enclosed in parentheses. Therefore, when we refer to the probability of event $B$ occurring, we write it as $P(B)$. This notation provides a clear and concise way to express the concept and is commonly adopted in both mathematics and statistics.

For instance, consider the scenario of rolling a fair six-sided die. If we want to calculate the probability of rolling a 3, we define event $B$ as “rolling a 3.” The probability of this event, $P(B)$, can be expressed as

This is because there is one favorable outcome (rolling a 3) out of six possible outcomes (the numbers 1 through 6).

Grasping this notation is essential, as it enables you to communicate and solve probability problems with greater efficiency. Whether you are working with straightforward events, such as rolling a die, or tackling more intricate scenarios, employing $P(B)$ helps you keep track of the probabilities involved. This notation is also foundational for more advanced concepts in probability, including conditional probability and independent events.