If a person throws $3$ dice,what is the probability that the sum of the numbers obtained is exactly $15$?

If $A_1, A_2, \ldots, A_{15}$ are the events of a random experiment,then which one of the following is true?

If the letters of the word "$ASSASSINATION$" are arranged at random in a row,then the probability that no two $A$'s come together is equal to

$A$ bag contains $a$ white and $b$ black balls. Two players $A$ and $B$ alternately draw a ball from the bag,replacing the ball each time after the draw,until one of them draws a white ball and wins the game. $A$ begins the game. If the probability of $A$ winning the game is three times that of $B$,then the ratio $a : b$ is

In a game of cards,what is the probability that a specific player holds all $4$ kings in a hand of $13$ cards?

Four numbers are chosen at random (without replacement) from the set $\{1, 2, 3, ..., 20\}$.
Statement-$1$: The probability that the chosen numbers when arranged in some order will form an $A.P.$ is $\frac{1}{85}$.
Statement-$2$: If the four chosen numbers form an $A.P.$,then the set of all possible values of common difference is $\{\pm 1, \pm 2, \pm 3, \pm 4, \pm 5, \pm 6\}$.