Question 395635
The boy says that he has x brothers and x sisters, so there are x+1 boys and x girls. The sister says that she has 2y brothers and y sisters, so 2y boys and y+1 girls. These numbers differ by 1, so


2y = x+1
y+1 = x


Solving, we get y = 2, so there are 3 girls and 4 boys.