Probability

Definition

Probability measures the likelihood of an event occurring, expressed as a number between 0 and 1. A probability of 0 means the event will not happen, while a probability of 1 means it will definitely happen.

5 Must Know Facts For Your Next Test

1. Probability is calculated as the ratio of the number of favorable outcomes to the total number of possible outcomes.
2. The sum of probabilities for all possible outcomes in a sample space is always 1.
3. The probability of the complement of an event is equal to 1 minus the probability of the event itself.
4. In mutually exclusive events, the probability that one or another occurs is the sum of their individual probabilities.
5. Independent events have no effect on each other's probabilities; thus, the probability of both occurring is the product of their individual probabilities.

Review Questions

• What does a probability value closer to 0 indicate about an event?
• How do you calculate the probability of two independent events both occurring?
• If you know P(A) and P(A'), how can you find one if you have the other?

Related terms

Sample Space:

The set of all possible outcomes in a probability experiment

Complementary Events: Two events are complementary if they are mutually exclusive and exhaustive; together they cover all possible outcomes

Mutually Exclusive Events: Two events that cannot occur at the same time