Two dice are thrown. The probability that the sum of the points on two dice will be $7$ is:

Three persons $P, Q$ and $R$ independently try to hit a target. If the probabilities of their hitting the target are $\frac{3}{4}, \frac{1}{2}$ and $\frac{5}{8}$ respectively,then the probability that the target is hit by $P$ or $Q$ but not by $R$ is

Three coins are tossed once. Find the probability of getting no head.

Let $N$ be the sum of the numbers appeared when two fair dice are rolled and let the probability that $N - 2, \sqrt{3N}, N + 2$ are in geometric progression be $\frac{k}{48}$. Then the value of $k$ is

Let $E_1, E_2, E_3$ be three arbitrary events of a sample space $S$. Which of the following statements is correct?

Three dice are thrown simultaneously. What is the probability of obtaining a total of $17$ or $18$?