In the family there are $\"\"$ children.

List the possible out comes is $\"\"$ .

The number of all possible out comes is $\"\"$ .

The number of ways that $\"\"$ boys can occur in a $\"\"$ child family is $\"\"$ .

All the events are equally likely events.

Let $\"\"$ be the event of $\"\"$ boys can occur in a $\"\"$ -child family.

The probability of $\"\"$ for equally likely outcomes is defined as and it is denoted by $\"\"$ .

$\"\"$

$\"\"$ .

The probability of having $\"\"$ boys in a $\"\"$ -child family is $\"\"$ .