Probability Calculator
Calculate probabilities, permutations, and combinations instantly.
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Frequently Asked Questions
What is the difference between permutations and combinations? +
Permutations count arrangements where order matters (e.g., picking 1st, 2nd, 3rd place). Combinations count selections where order doesn't matter (e.g., choosing a committee). nPr = n!/(n-r)! and nCr = n!/[r!(n-r)!].
What is conditional probability? +
Conditional probability is the probability of event A occurring given that event B has already occurred. It's written as P(A|B) and calculated as P(A and B) / P(B).
How do you calculate the probability of two events? +
For the union (A or B): P(A or B) = P(A) + P(B) - P(A and B). For independent events, P(A and B) = P(A) × P(B). For mutually exclusive events, P(A or B) = P(A) + P(B).
What is the complement of an event? +
The complement of event A is the probability that A does NOT occur. It equals 1 - P(A). For example, if the probability of rain is 0.3, the probability of no rain is 0.7.
What values can probability have? +
Probability always ranges from 0 to 1 (or 0% to 100%). A probability of 0 means the event is impossible, and 1 means it is certain. Values outside this range are not valid probabilities.
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