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

$A$ bag contains $3$ white,$3$ black,and $2$ red balls. Three balls are drawn one by one without replacement. The probability that the third ball is red is:

The probability that a contractor will get a plumbing contract is $2/3$ and the probability that he will not get an electric contract is $5/9$. If the probability of getting at least $1$ contract is $4/5$,what is the probability that he will get both?

$2$ dice are thrown. Find the probability of getting an odd number on $1$ die and a multiple of $3$ on the other.

$A$ box contains $5$ red,$4$ green and $3$ black balls. $3$ balls are drawn at random. What is the probability that they are not of the same colour?

$A$ can hit a target $4$ times in $5$ shots,$B$ can hit a target $3$ times in $4$ shots,and $C$ can hit a target $2$ times in $3$ shots. All three fire a shot each. What is the probability that at least two shots hit the target?