# Binomial Practice

Algebra Level pending

For r= 0,1......,10 let $$A_{r},B_{r},C_{r}$$ denote respectively the coefficients of $$x^r$$ in the expansions of $$(1+x)^{10},(1+x)^{20}$$ and $$(1+x)^{30}$$ then ; $$\displaystyle \sum_{r=1} ^{10} A_{r}(B_{10}B_{r} - C_{10}A_{r})$$ is :

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