Probability Calculator
Calculate probabilities for single, combined, and conditional events.
Understanding Probability
Probability is a number between 0 and 1 that represents how likely an event is to occur. A probability of 0 means the event is impossible, while 1 means it is certain.
Coin flip example: A fair coin has 1 favorable outcome (heads) out of 2 total outcomes, giving P(heads) = 1/2 = 0.5 = 50%.
Dice example: Rolling a 6 on a fair die: P(6) = 1/6 ≈ 0.167 = 16.7%. Rolling an even number: P(even) = 3/6 = 0.5 = 50%.
Combined events: For independent events, P(A and B) = P(A) × P(B). For example, rolling two sixes in a row: 1/6 × 1/6 = 1/36 ≈ 2.78%.
Bayes' Theorem lets you reverse conditional probabilities: P(A|B) = P(B|A) × P(A) / P(B). It is fundamental to medical testing, spam filtering, and machine learning.