Probability, nCr & nPr

Probability Calculator

Compute simple event probability, or count combinations and permutations, all instantly and privately in your browser.

How it works

1

Choose a mode

Pick simple probability for a single event, or nCr/nPr for counting problems.

2

Enter your numbers

Type outcomes or set size and selection count — results update as you go.

3

Read every format

See the result as a fraction, decimal, percent or exact count, whichever fits the mode.

FAQ

What is the difference between a combination and a permutation?

A combination (nCr) counts groupings where order doesn't matter, like picking a committee. A permutation (nPr) counts arrangements where order does matter, like ranking finishers in a race.

What are odds in favor of an event?

Odds in favor compare favorable outcomes to unfavorable outcomes, written as favorable:unfavorable. This differs from probability, which compares favorable outcomes to all possible outcomes.

Can r be larger than n?

No. Both nCr and nPr require r to be less than or equal to n, since you can't choose or arrange more items than are available in the set.

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