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Subject:  Precalculus

Compute the permutations 7P3

Count the number of ordered arrangements of 3 items chosen from 7.

Answer nPr = 210, nCr = 35

Solution

  1. Given n = 7, r = 3
  2. Permutations nPr = n! / (n − r)! = 7! / 4! = 210
  3. Combinations nCr = n! / (r!·(n − r)!) = nPr / r! = 210 / 6 = 35
  4. Factorial n! = 5040

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