p(n,r) represents the number of permutations of 'r' items selected from a total of 'n' distinct items. This concept is crucial in understanding how arrangements can be made, emphasizing the significance of order when selecting items. The formula for calculating p(n,r) is given by $$p(n,r) = \frac{n!}{(n-r)!}$$, where 'n!' denotes the factorial of 'n', reflecting the product of all positive integers up to 'n'.
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