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Problem from China Olympiad

What does the capital C symbol mean?

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1 Answer

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It is the binomial coefficient. There are 3 ways to write it in China:

• In mainland, we prefer$$C_n^r=\frac{n!}{r!(n-r)!}.$$

• In Hong Kong, we prefer$$nCr=C_r^n=\frac{n!}{r!(n-r)!}.$$

All are acceptable.

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