SOLUTION: If nPr = 120, and nCr=20, then determine the value of 7Pr.

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Question 386769: If nPr = 120, and nCr=20, then determine the value of 7Pr.
Found 2 solutions by jim_thompson5910, solver91311:
Answer by jim_thompson5910(35256) About Me  (Show Source):
You can put this solution on YOUR website!
Hint: Use the idea that n P r = r! * (n C r)

Answer by solver91311(24713) About Me  (Show Source):
You can put this solution on YOUR website!


The difference between a Permutation of n things taken r at a time and a Combination of n things taken r at a time is a factor equal to the number of ways that you can order the r things, that is to say r!. Hence:



So for your problem,



And then you need the value of:



The arithmetic is yours to do.

John

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