Probability of simple events
Probability is the chance that a certain event will happen. It is defined as the ratio of the number of ways a specific event -called a positive outcome - can happen to the total number of possible outcomes. That is:
What is the probability that a day of the week chosen at random will begin with the letter S?
There are two positive outcomes: Saturday and Sunday.
There are seven days in a week, so there are seven total possible outcomes.
Using the rule above, you can see that the probability is
The probability that a day chosen at random will begin with the letter S is
The possible outcomes of this experiment are yellow, blue, green, and red.