Let $S=\{1,2,3,5,7,10,11\}$. The number of nonempty subsets of $S$ that have the sum of all elements a multiple of $3$ , is $........$
$42$
$43$
$41$
$40$
If $^{n + 1}{C_3} = 2{\,^n}{C_2},$ then $n =$
The solution set of $^{10}{C_{x - 1}} > 2\;.{\;^{10}}{C_x}$ is
A group of $9$ students, $s 1, s 2, \ldots, s 9$, is to be divided to form three teams $X, Y$ and, $Z$ of sizes $2,3$ , and $4$, respectively. Suppose that $s_1$ cannot be selected for the team $X$, and $s_2$ cannot be selected for the team $Y$. Then the number of ways to form such teams, is. . . .
Value of $r$ for which $^{15}{C_{r + 3}} = {\,^{15}}{C_{2r - 6}}$ is
Determine $n$ if
$^{2 n} C_{3}:^{n} C_{3}=11: 1$