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why is nPk "n!/(n-k)!" ? i'm understanding that nPk = n*(n - 1)***(n - k + 1). uhh...
Quote: Originally Posted by miki why is nPk "n!/(n-k)!" ? i'm understanding that nPk = n*(n - 1)***(n - k + 1). uhh... $\displaystyle N!=N\cdot(n-1)\cdots(N-k+1)(N-k)!$ Example $\displaystyle _{10}P_4=10\cdot 9\cdot 8\cdot 7=\frac{10!}{(10-4)!}$
thanks a lot ! i understod your reply meaning. i try it!