From a pack of $52$ cards,two cards are drawn in succession one by one without replacement. The probability that both are aces is

There are $3$ bags which are known to contain $2$ white and $3$ black balls; $4$ white and $1$ black balls and $3$ white and $7$ black balls respectively. $A$ ball is drawn at random from one of the bags and found to be a black ball. Then the probability that it was drawn from the bag containing the most black balls is

$A$ bag contains $19$ tickets numbered from $1$ to $19$. $A$ ticket is drawn and then another ticket is drawn without replacement. The probability that both the tickets will show even numbers is:

$A$ person draws a card from a pack of playing cards,replaces it and shuffles the pack. He continues doing this until he draws a spade. The chance that he will fail in the first two attempts is

The probability of a sure event is

$A$ couple has two children. If at least one of them is a boy,what is the probability that the other is also a boy?