Question:
If 2nC3 : nC2 = 44 : 3, find n.
Solution:
Given: $2 n_{C_{3}}: n_{C_{2}}=44: 3$
$\frac{2 n_{C_{3}}}{n_{C_{2}}}=\frac{44}{3}$
$\Rightarrow \frac{2 n !}{3 !(2 n-3) !} \times \frac{2 !(n-2) !}{n !}=\frac{44}{3}$
$\Rightarrow \frac{2 n(2 n-1)(2 n-2)}{3 n(n-1)}=\frac{44}{3}$
$\Rightarrow(2 n-1)(2 n-2)=22(n-1)$
$\Rightarrow 4 n^{2}-6 n+2=22 n-22$
$\Rightarrow 4 n^{2}-28 n+24=0$
$\Rightarrow n^{2}-7 n+6=0$
$\Rightarrow n^{2}-6 n-n+6=0$
$\Rightarrow n(n-6)-1(n-6)=0$
$\Rightarrow(n-1)(n-6)=0$
$\Rightarrow n=1$ or, $n=6$
Now, $n=1 \Rightarrow 2_{C_{3}}: 2_{C_{2}}=44: 3$
But, this is not possible.
$\therefore n=6$