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1. The problem statement, all variables and given/known data

n!/(n-r)! = n(n-1)(n-2)...(n-r+1)

where r is the number of objects we want from n distinct objects (3 billiard balls out of 16)

I don't understand what the last term in the expansion means, the (n-r+1). For example, suppose we have 5 distinct objects and we want to choose 2. This means that n = 5 and r = 2

5x4x3x2x1x(5-2+1)

is this correct?

Thank you for your help

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# Homework Help: N factorial - general question

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