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If the coefficients of the $r$th term and the $(r+1)$th term in the expansion of $(1+x)^{20}$ are in the ratio $1:2$, then $r$ equals

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$\dfrac{\binom{n}{r-1}}{\binom{n}{r}} = \dfrac{r}{n-r+1}$. Use this ratio formula directly to avoid computing individual binomial coefficients.

Updated On: Apr 8, 2026

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The Correct Option is B

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If the coefficients of the $r$th term and the $(r+1)$th term in the expansion of $(1+x)^{20}$ are in the ratio $1:2$, then $r$ equals

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The Correct Option is B

Solution and Explanation

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