Let $S$ be the sample space of the random experiment of throwing simultaneously two unbiased dice and $E_k = \{(a, b) \in S : ab = k\}$. If $p_k = P(E_k)$, then which of the following is correct?

$A$ student appears for tests $I$, $II$, and $III$. The student is successful if they pass in tests ($I$ and $II$) $OR$ ($I$ and $III$). The probabilities of the student passing in tests $I$, $II$, and $III$ are respectively $p$, $q$, and $1/2$. If the probability of the student being successful is $1/2$, then:

Four coins are tossed. The probability that at least one head turns up is:

The probability of getting at least one tail in $4$ throws of a coin is

$A$ coin is tossed twice. The probability of getting head both the times is

If one ticket is selected at random from $30$ tickets,each with a distinct number from $1$ to $30$,then the probability that the number on the selected ticket is a multiple of $3$ or $5$ is