Chapter 3: Probability 3.7: Permutations and Combinations

items out of n possibilities (instead of 3 out of 25 or 3 out of 8 as in the previous examples), the number of possible arrangements will be given by . n · (n – 1) · (n – 2) ··· (n – r + 1) If you don’t see why (n — r + 1) is the right number to use for the last factor, just think back to the first example in this section, where ... ................
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