How many three letter combinations can be formed from the letters "defgh" if no letter can be used more than once. I think this is the answer: P(5!, 3!) = 5!/3! = 5 * 4 * 3! * 2!/3! * 2! = 5 * 4 = 20 Is this right?
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If order matters, then P(5,3)=60. If order doesn't matter, then C(5,3)=10 $\displaystyle P(n,k)=\frac{n!}{(n-k)!}$ $\displaystyle C(n,k)=\frac{n!}{(n-k)!k!}$
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