Ways Counter: Combinations, Permutations and the Chance of One

Items to choose from (n)

How many chosen (k)

Does the order matter?

Can an item repeat?

Different guesses allowed for the chance of hitting one

Load an example from the book

Enter your numbers, then press Calculate.

From the book, Chapter 2. Picking two friends from six for concert tickets: 15 pairs, so any one pair is 1 in 15; in order there are 30. A thief with three guesses at a four-digit PIN has 0.03% (1 in 3,333). Six numbers from 49: 13,983,816 tickets. Five people can sit in a row 120 ways, and a deck can be shuffled into 8.07 × 10⁶⁷ orders.

Exact arithmetic, worked the way the book shows. Everything stays in your browser: no sign-up, nothing stored or sent.