[JEE Advanced 1979] if binom n r 1 36 binom nr 84 and binom n r 1
If $\binom n{r-1}=36,\ \binom nr=84$ and $\binom n{r+1}=126$, then $r$ is
(a) $1$
(b) $2$
(c) $3$
(d) none of these
1 Answer
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✓ Vidaara Team
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· 2d ago
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Correct answer: (c) $3$
$\frac{\binom nr}{\binom n{r-1}}=\frac{n-r+1}r=\frac73$ and $\frac{\binom n{r+1}}{\binom nr}=\frac{n-r}{r+1}=\frac32$ give $n=9,r=3$.
JEE Advanced 1979 · Permutations and Combinations — verified solution by the Vidaara Team.
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