Probability Calculator
About Probability Calculator
Understanding Probability
Probability measures the likelihood of an event occurring, expressed as a number between 0 (impossible) and 1 (certain), or equivalently 0% to 100%. It underpins statistics, gambling, insurance, weather forecasting, medical testing, risk assessment, and decision-making. Basic probability equals favorable outcomes divided by total possible outcomes for equally likely events.
Key Probability Rules
Complement: P(not A) = 1 - P(A). Union (OR): P(A or B) = P(A) + P(B) - P(A and B). Intersection (AND): For independent events, P(A and B) = P(A) x P(B). Conditional: P(A|B) = P(A and B) / P(B). Understanding these rules allows you to calculate complex probabilities from simpler ones.
How to Use This Calculator
Enter the probability of events as decimals, fractions, or percentages. Choose the type of calculation (single event, AND, OR, conditional, complement). The calculator applies the correct rule and shows the result as probability, percentage, and odds. It also shows the formula used for educational purposes.
Frequently Asked Questions
What is the difference between odds and probability?
Probability = favorable/total outcomes (e.g., 1/6 for rolling a specific die number). Odds = favorable/unfavorable outcomes (e.g., 1:5 for the same event). Odds of 3:1 means probability of 3/4 = 75%.
What does independent mean in probability?
Two events are independent if the outcome of one does not affect the other. Coin flips are independent. Drawing cards without replacement are dependent (probabilities change).
Can probability be greater than 1?
No. Probability ranges from 0 to 1 (0% to 100%). If your calculation gives a value above 1, there is an error. Odds can be greater than 1 (e.g., 5:1), but odds are not the same as probability.
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