История изменений

https://en.wikipedia.org/wiki/Boy_or_Girl_paradox#Analysis_of_the_ambiguity

From all families with two children, at least one of whom is a boy, a family is chosen at random. This would yield the answer of 1/3.

From all families with two children, one child is selected at random, and the sex of that child is specified to be a boy. This would yield an answer of 1/2.[3][4]

https://en.wikipedia.org/wiki/Boy_or_Girl_paradox#Analysis_of_the_ambiguity