Question

If ${{}^{n}C}_8={{}^{n}C}_7$, then $n=$

Answer 1

In a binomial expression,

We know that ${}^n{C}_r={}^n{C}_{n-r}$

So when ${}^n{C}_8={}^n{C}_7$

Here, $r=8$ and $n-r=7$

$\Rightarrow n-8=7\Rightarrow n=7+8$

$\Rightarrow n=15$