In a single throw of $2$ dice,what is the probability of getting a total of $7$?

In a single throw of $3$ dice,find the probability of getting a total of $17$ or $18$.

$A$ bag $X$ contains $2$ white and $3$ black balls and another bag $Y$ contains $4$ white and $2$ black balls. One bag is selected at random and a ball is drawn from it. Then the probability for the ball chosen to be white is

$A$ bag contains $4$ white balls and $2$ black balls. Another bag contains $3$ white balls and $5$ black balls. If one ball is drawn from each bag,then the probability that both the balls are black,is

The probability of an impossible event,i.e.,$P(\phi)$,is:

$A$ bag contains $3$ white and $5$ black balls. If one ball is drawn, then the probability that it is black, is