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raleung2
from a collection of 9 books, martin is asked to list his 5 favorites starting with his most favorite, second favorite, 3rd favorite and so on. How many ways can martin make his list?
\[9\times 8\times 7\times 6\times 5\]
\[nPr=\frac{n!}{(n-r)!}=\frac{9!}{4!}=9\times 8\times 7\times 6\times 5\]=15120 ways