In four schools ${B_1},{B_2},{B_3},{B_4}$ the percentage of girls students is $12, 20, 13, 17$ respectively. From a school selected at random, one student is picked up at random and it is found that the student is a girl. The probability that the school selected is ${B_2},$ is

Two friends $A$ and $B$ have equal number of daughters. There are three cinema tickets which are to be distributed among the daughters of $A$ and $B$. The probability that all the tickets go to daughters of $A$ is $1/20$. The number of daughters each of them have is

Three of the six vertices of a regular hexagon are chosen at random. The probability that the triangle with these three vertices is equilateral, is equal to

Three squares of a chess board are chosen at random, the probability that two are of one colour and one of another is

Find the probability that when a hand of $7$ cards is drawn from a well shuffled deck of $52$ cards, it contains all Kings.

If a party of $n$ persons sit at a round table, then the odds against two specified individuals sitting next to each other are