There are $5$ white, $7$ red, $4$ black, and $2$ blue identical balls in a box. One ball is selected at random from the box. Find the probability that the ball is either black or white.

Two balanced dice are rolled simultaneously. Then,the probability that the sum of numbers on the dice is $11$ is .........

$A$ child's game has $8$ triangles of which $3$ are blue and the rest are red,and $10$ squares of which $6$ are blue and the rest are red. One piece is lost at random. Find the probability that it is a
$(i)$ triangle
$(ii)$ square
$(iii)$ square of blue colour
$(iv)$ triangle of red colour

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

$A$ box contains $5$ red,$8$ white,and $4$ green balls. If a ball is drawn at random from the box,find the probability that the ball drawn is red.

An event is very unlikely to happen. Its probability is closest to