In a lottery there are $10$ prizes and $25$ blanks. What is the probability of getting a prize?

$17$ cards numbered $1,2,3,4,......,17$ are put in a box and mixed thoroughly. A card is drawn at random from the box. Find the probability that the card drawn bears an odd number.

$17$ cards numbered $1,2,3,4,......,17$ are put in a box and mixed thoroughly. A card is drawn at random from the box. Find the probability that the card drawn bears a number divisible by $5$. 

In a family of $3$ children, Find the probability of having at least one boy.

A bag contains $4$ white balls, $5$ red balls, $2$ black balls and $4$ green balls. A ball is drawn at random from the bag.Find the probability that it is not green. If the probability is $\frac{a}{b}$, find $a$.

If the answer is of the form $\frac{a}{b}$, then what is the value of $a$?