If $\frac{{{}^{n + 2}{C_6}}}{{{}^{n - 2}{P_2}}} = 11$, then $n$ satisfies the equation
$n^2 + n - 110 =0$
$n^2 + 2n - 80 =0$
$n^2 +3n- 108=0$
$n^2 + 5n - 84 =0$
If $^{10}{C_r}{ = ^{10}}{C_{r + 2}}$, then $^5{C_r}$ equals
$^n{C_r}\,{ \div ^n}{C_{r - 1}} = $
How many numbers of $6$ digits can be formed from the digits of the number $112233$
There are $m$ books in black cover and $n$ books in blue cover, and all books are different. The number of ways these $(m+n)$ books can be arranged on a shelf so that all the books in black cover are put side by side is
If $^{20}{C_{n + 2}}{ = ^n}{C_{16}}$, then the value of $n$ is