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Q. If $ ^{2n+3}C_{2n} - \,{}^{2n+2}C_{2n-1} = 15 \left(2n+1\right)$, then $n= $

Permutations and Combinations

Solution:

$\frac{\lfloor2n+3 }{\lfloor2n \lfloor3} -\frac{ \lfloor2n+2}{\lfloor2n-1\lfloor3} = 15\left(2n+1\right) $
$ \Rightarrow \frac{\left(2n+2\right)\left(2n+1\right)}{2} = 15\left(2n+1\right) $
$ \Rightarrow n+1=15$
$\Rightarrow n=14.$