What does (9 over 3) mean? I can't type the exact operation; please see attached. Or can you direct me to a site where this operation is explained?
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I think the answer is: Binomial coefficient – Feb 22 '15 at 00:35
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If the notation is $\binom93$ then it's certainly a binomial coefficient. – hmakholm left over Monica Feb 22 '15 at 00:38
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1... and does this book not explain this notation somewhere earlier? – GEdgar Feb 22 '15 at 00:51
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This is a notation that stands for "9 choose 3"
You probably know it as $${9 \choose 3 }= \ _9C_3$$
hyg17
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$\dbinom 9 3$, pronounced "nine choose three", is the number of subsets of size $3$ of a set of size $9$.
This can be shown to be $\dfrac{9\cdot8\cdot7}{3\cdot2\cdot1} = 3\cdot4\cdot7=84$.
