Calculate probability

Calculate single-event and repeated independent-trial probabilities from equally likely outcomes.

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ToolProbability Calculator
Input
Output
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Preview

How it works

One-trial success is favourable outcomes ÷ total outcomes. Repeated results use pⁿ for all successes, (1−p)ⁿ for all failures, 1−(1−p)ⁿ for at least one success, and n × p for the expected successes.

  • Trials are independent and identically distributed.
  • No unequal outcome weights are inferred.

Worked example

Two independent events
A 50% chance and a 30% chance
Input
											Probability a: 0.5
Probability b: 0.3
Output
												Complement a: 0.5
Complement b: 0.7
Both occur: 0.15
Either occurs: 0.65

When to use this

Fair-die exercises ask for at least one six, component models estimate repeated failure chances, and binomial lessons check expected successes.

Edge cases

  • Drawing cards without replacement changes p between trials and violates the independence assumption.
  • Outcomes with unequal weights cannot use favourable divided by total.
  • At least one success uses a complement; multiplying n by p gives an expectation, not that event’s probability.