If the events $A$ and $B$ are mutually exclusive,then $P\left( \frac{A}{B} \right) = $

$A$ bag contains $8$ black and $7$ white balls. Two balls are drawn at random. For which of the following is the probability the highest?

In a simultaneous throw of $2$ dice,find $P(A \text{ or } B)$ if $A$ denotes the event 'a total of $11$' and $B$ denotes the event 'an odd number on each die'.

Two dice are thrown. If the first die shows $5$,then the probability that the sum of the numbers on both dice is $8$ or more than $8$ is:

From a pack of $52$ cards,one card is drawn at random. The probability that it is either a king or a queen is:

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