Question 1

What is a permutation?

Accepted Answer

A permutation (nPr) is the number of ways to arrange r items from a set of n, where order matters. The formula is nPr = n! / (n - r)!. For example, P(5,3) = 60 ways to arrange 3 items from 5.

Question 2

What is a combination?

Accepted Answer

A combination (nCr) is the number of ways to choose r items from a set of n, where order does not matter. The formula is nCr = n! / (r! × (n - r)!). For example, C(5,3) = 10 ways to pick 3 items from 5.

Question 3

What does repetition mean?

Accepted Answer

With repetition, the same item can be chosen multiple times. The formulas become nPr_repeated = n^r and nCr_repeated = (n + r - 1)! / (r! × (n - 1)!). Without repetition is the standard case where each item is used at most once.

Question 4

How large a number can this handle?

Accepted Answer

JavaScript numbers handle integers up to 2^53 - 1 (about 9 quadrillion) precisely. For larger results, the calculator automatically uses BigInt to give exact values. Factorials of n > 1000 are usually astronomical and are returned in scientific notation.

Permutation (nPr)

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