If six students, including two particular students $A$ and $B,$ stand in a row, then the probability that $A$ and $B$ are separated with one student in between them is
$\frac {8}{15}$
$\frac {4}{15}$
$\frac {2}{15}$
$\frac {1}{15}$
The letter of the word `$ASSASSIN$' are written down at random in a row. The probability that no two $S$ occur together is
Five numbers $x _{1}, x _{2}, x _{3}, x _{4}, x _{5}$ are randomly selected from the numbers $1,2,3, \ldots \ldots, 18$ and are arranged in the increasing order $\left( x _{1}< x _{2}< x _{3}< x _{4}< x _{5}\right)$. The probability that $x_{2}=7$ and $x_{4}=11$ is
Out of $30$ consecutive numbers, $2$ are chosen at random. The probability that their sum is odd, is
In a certain lottery $10,000$ tickets are sold and ten equal prizes are awarded. What is the probability of not getting a prize if you buy one ticket.
$n$ cadets have to stand in a row. If all possible permutations are equally likely, then the probability that two particular cadets stand side by side, is