Calculate the probability of a single event, or the combined probability of two independent events.
This tool calculates the probability of one or more events occurring, including single events, combined events (AND/OR), and conditional probability. It's used in statistics coursework, games of chance, risk assessment, and decision-making under uncertainty.
Basic probability: P(event) = Favorable outcomes รท Total possible outcomes. For independent events: P(A and B) = P(A) ร P(B). For either event occurring: P(A or B) = P(A) + P(B) โ P(A and B).
Enter the number of favorable outcomes and total possible outcomes for a single event, or enter multiple event probabilities to calculate combined probabilities.
Example: The probability of rolling a 4 on a standard six-sided die is 1/6 โ 16.67%. The probability of rolling two 4s in a row (independent events) is (1/6) ร (1/6) = 1/36 โ 2.78%.
What's the difference between independent and dependent events? Independent events don't affect each other's outcome (like separate coin flips), while dependent events do โ the probability of a dependent event changes based on what already happened (like drawing cards without replacement).
Why is probability always between 0 and 1? A probability of 0 means an event is impossible, and 1 means it's certain, so all real probabilities fall somewhere within this range representing degrees of likelihood โ probabilities are also often expressed as percentages (0% to 100%).
What's the difference between "and" and "or" in probability? "And" typically requires multiple events to all happen (usually multiplied together), while "or" means at least one of the events happens (typically added together, adjusted to avoid double-counting overlap).
What is conditional probability? Conditional probability calculates the likelihood of an event given that another event has already occurred, written as P(A|B), which is especially important when events are not independent of each other.
How is probability used in real-world decision-making? Probability underlies insurance pricing, weather forecasting, medical risk assessment, financial modeling, and game design, helping quantify uncertainty to support informed decisions.