When do I use nCr = n!/[r!(n−r)!] in Permutations & Combinations, and what does it mean?
number of unordered selections of r from n.
nCr = n!/[r!(n−r)!] — number of unordered selections of r from n. Use it when: order does not matter. Always check the condition holds before plugging in numbers.
Key point
nCr = n!/[r!(n−r)!]
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