9. Petya has as many sisters as brothers, while his sister Ira has twice as few sisters as brothers. How many boys and how many girls are there in this family?
9. If there are $x$ girls, then there are $x+1$ boys. Without Irina, there will be $x-1$ girls, then from the condition we have

$$
2(x-1)=x+1
$$

from which $x=3$. Therefore, there are 3 girls and 4 boys in the family.