From $21$ tickets numbered $1, 2, 3, \ldots, 21$,one ticket is drawn at random. Find the probability that the ticket drawn has a number divisible by $3$.

$1$ bag contains $4$ white and $2$ black balls. Another bag contains $3$ white and $5$ black balls. If $1$ ball is drawn from each bag,find the probability that both balls are black.

Two dice are thrown. Find the probability of getting an even number as the sum.

$A$ and $B$ are two events such that $P(A) = 0.8$,$P(B) = 0.6$,and $P(A \cap B) = 0.5$. Then the value of $P(A/B)$ is:

Seven white balls and three black balls are randomly placed in a row. The probability that no two black balls are placed adjacently equals

$A$ card is drawn from a well-shuffled pack of $52$ cards. The probability of getting a queen of clubs or a king of hearts is: