SOLUTION: simplify (n-1)C(r-1) + (n-1)Cr

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Question 594320: simplify (n-1)C(r-1) + (n-1)Cr
Answer by richard1234(7193) About Me  (Show Source):
You can put this solution on YOUR website!
Pascal's triangle. It can be proven using a committee-forming argument (suppose you choose r people from a group of n. If person X is chosen, we have to choose r-1 people from n-1. If X is not chosen, we choose r people from n-1).



You can also do it algebraically.