Six boys and six girls sit in a row. What is the probability that the boys and girls sit alternatively?

Four cards are drawn at random from a pack of $52$ playing cards. What is the probability that one card is drawn from each suit?

There are $10$ bulbs in a room,out of which $4$ are defective. If $3$ bulbs are chosen at random,what is the probability that the room will be illuminated? (The room is illuminated if at least one bulb is good.)

$A$ committee consists of $9$ experts taken from three institutions $A, B$,and $C$,of which $2$ are from $A$,$3$ from $B$,and $4$ from $C$. If three experts resign,then the probability that they belong to different institutions is

From a collection of eight cards numbered $1$ to $8$,if two cards are drawn at random,one after the other with replacement,then the probability that the product of the numbers that appear on the cards is a perfect square is

From $3n$ consecutive integers, three integers are selected at random. The probability that their sum is divisible by $3$ is