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Probability Calculator

Calculate probability of events and combined probabilities.

Results

P(Event 1)0.3
P(Event 2)0.4
P(E1 AND E2)0.12
P(E1 OR E2)0.58

What is Probability?

Probability measures how likely an event is to occur, expressed as a number between 0 (impossible) and 1 (certain). It's fundamental to statistics, gambling, insurance, weather forecasting, and decision-making.

Formula

P(Event) = Favorable Outcomes / Total Outcomes
P(A AND B) = P(A) × P(B) (independent events)
P(A OR B) = P(A) + P(B) − P(A AND B)
P(NOT A) = 1 − P(A)

How to use this Probability Calculator?

1. Enter favorable and total outcomes for Event 1. 2. Enter the same for Event 2 (for combined probability). 3. See individual and combined probabilities.

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Frequently asked questions

What is the probability of rolling a 6?
P(6) = 1/6 = 0.1667 = 16.67%. A fair die has 6 equally likely outcomes.
What is the probability of heads twice in a row?
P(HH) = 1/2 × 1/2 = 1/4 = 0.25 = 25%. Each flip is independent.
What is Bayes' theorem?
Bayes' theorem calculates conditional probability: P(A|B) = P(B|A) × P(A) / P(B). It's used in medical testing, spam filters, and machine learning.

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Standard Deviation CalculatorPermutation & Combination CalculatorConfidence Interval Calculator
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