The probability of an event, E, is the likelihood that E will occur. "Likelihood" is normally represented as a percentage or a fraction between 0 and 1. We compute the probability of an event by dividing the number of ways the event under consideration may occur by the total possible number of events.

Let the event of selecting a weekday be denoted by W.

The days under consideration are the 5 weekdays, Mon., Tues., Wed., Thurs. and Fri. The total number of possible selections is the number of days in the week which equals 7. Therefore the probability of selecting a weekday (denoted P(W)) equals 5/7.