$2$ dice are thrown. Find the probability of getting a doublet of even numbers.

The probabilities of winning the race by two athletes $A$ and $B$ are $\frac{1}{5}$ and $\frac{1}{4}$ respectively. The probability of winning by neither of them is:

$A$ 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?

Three letters are to be sent to different persons,and addresses on the three envelopes are also written. Without looking at the addresses,the probability that all the letters go into the right envelope is equal to

An integer is chosen at random and squared. The probability that the last digit of the square is $1$ or $5$ is

Suppose $n \ge 3$ persons are sitting in a row. Two of them are selected at random. The probability that they are not together is