When do I use nPr = n!/(n−r)! in Permutations & Combinations, and what does it mean?
number of ordered arrangements of r from n.
nPr = n!/(n−r)! — number of ordered arrangements of r from n. Use it when: order matters, no repetition. Always check the condition holds before plugging in numbers.
Key point
nPr = n!/(n−r)!
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