The event $A$ is independent of itself if and only if $P(A) = $

Out of $5$ girls and $3$ boys,$4$ children are to be randomly selected for a quiz contest. What is the probability that all the selected children are girls?

One ticket is selected at random from $100$ tickets numbered $00, 01, 02, \dots, 98, 99$. If $X$ and $Y$ denote the sum and the product of the digits on the tickets respectively,then $P(X = 9 | Y = 0)$ equals:

You are given the digits $2, 3, 4, 6,$ and $7$. In how many ways can you form a $3$-digit number without repetition of digits that is odd and greater than $300$?

The probability of getting at least one tail in $4$ throws of a coin is

Three letters are to be sent to different persons,and addresses on the three envelopes are also written. Without looking at the addresses,the probability that all the letters go into the right envelope is equal to