Fifteen persons,including $A$ and $B$,sit down at random at a round table. The probability that there are $4$ persons between $A$ and $B$ is

For two events $A$ and $B$,if $P(A) = P(A|B) = \frac{1}{4}$ and $P(B|A) = \frac{1}{2}$,then

$A$ card is drawn from a pack of $100$ cards numbered $1$ to $100$. Find the probability of drawing a number which is a square.

An urn contains $10$ green,$12$ yellow,and $11$ white balls. What is the probability that when $2$ balls are selected,at least one is white?

$2$ dice are rolled together. What is the probability that the sum of the $2$ numbers is divisible by $3$ or by $4$?

There are $3$ urns $A, B$,and $C$. Urn $A$ contains $4$ red balls and $3$ black balls. Urn $B$ contains $5$ red balls and $4$ black balls. Urn $C$ contains $4$ red balls and $4$ black balls. One ball is drawn from each of these urns. What is the probability that the $3$ balls drawn consist of $2$ red balls and $1$ black ball?