$3$ coins are tossed. Find the probability of getting at least $1$ head and $1$ tail.

$A$ husband and wife appear in an interview for $2$ vacancies in the same post. The probability of husband's selection is $\frac{1}{7}$ and that of wife's is $\frac{1}{5}$. What is the probability that none of them will be selected?

If two regular six-sided dice are thrown,the probability that the sum will be a prime number is

The probability of happening an event $A$ is $0.5$ and that of $B$ is $0.3$. If $A$ and $B$ are mutually exclusive events,then the probability of happening neither $A$ nor $B$ is

$A$ bag $x$ contains $3$ white balls and $2$ black balls and another bag $y$ contains $2$ white balls and $4$ black balls. $A$ bag and a ball out of it are picked at random. The probability that the ball is white,is

There are $n$ letters and $n$ addressed envelopes. The probability that each letter is placed in the correct envelope is: