Two dice are thrown together. The probability that at least one will show its digit $6$ is

$A$ problem in Statistics is given to four students $A, B, C$ and $D$. Their chances of solving it are $\frac{1}{3}, \frac{1}{4}, \frac{1}{5}$ and $\frac{1}{6}$ respectively. What is the probability that the problem will be solved?

$A$ problem of mathematics is given to three students whose chances of solving the problem are $\frac{1}{3}$,$\frac{1}{4}$,and $\frac{1}{5}$ respectively. The probability that the question will be solved is

There are $4$ envelopes with addresses and $4$ corresponding letters. The probability that no letter goes into its correct envelope 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

Two coins are tossed. Find the probability that two heads are obtained.