A mother and her friend are talking about how many chidren they have. The friend knows how many daughters the mother has, but doesn't know how many sons she has. The mother says:
"All of my children have the same amount of brothers and the same amount of sisters as the other children."
Now the friend knew how many sons she had. How many sons did the mother have?
If the mother has no daughters, then the number of sons can be 0 to infinity, because each would have the same number of brothers. If the mother has daughters, however, she can't have any sons because every son would have 1 less brother than the sister and every daughter 1 less sister than the brothers.
Sons or daughters
