An unbiased coin is tossed thrice. Find the probability of the following event:
$B:$ at least $2$ heads are received.

$A$ balanced die is thrown. Find the probability that the number on the die is even.

If a number is selected at random from one-digit natural numbers,the probability of that number being a multiple of $3$ is ..... .

Two balanced dice are rolled simultaneously. Then,the probability that the sum of numbers on the dice is $8$ is ........

There are $1000$ sealed envelopes in a box,$10$ of them contain a cash prize of $Rs. 100$ each,$100$ of them contain a cash prize of $Rs. 50$ each,$200$ of them contain a cash prize of $Rs. 10$ each,and the rest do not contain any cash prize. If they are well shuffled and an envelope is picked out,what is the probability that it contains no cash prize?

There are boards numbered $1$ to $50$ in a box. One board is selected at random. Find the probability that the number on the board is a multiple of $10$. (in $/10$)