Parade on MSN: This is hands-down the best girls’ trip destination right now—and it isn’t Vegas This is hands-down the best girls’ trip destination right now—and it isn’t Vegas A couple decides to keep having children until they have the same number of boys and girls, and then stop. Assume they never have twins, that the "trials" are independent with probability 1/2 of a boy, and that they are fertile enough to keep producing children indefinitely. Expected girls from one couple$ {}=0.5\cdot1 + 0.25\cdot1 =0.75$ Expected boys from one couple$ {}=0.25\cdot1 + 0.25\cdot2 =0.75$ 1 As I said this works for any reasonable rule that could exist in the real world.
An unreasonable rule would be one in which the expected children per couple was infinite. Expected number of ratio of girls vs boys birth - Cross Validated Probability of having 2 girls and probability of having at least one girl Ask Question Asked 8 years, 7 months ago Modified 8 years, 7 months ago Probability of having 2 girls and probability of having at least one girl 1st 2nd boy girl boy seen boy boy boy seen girl boy The net effect is that even if I don't know which one is definitely a boy, the other child can only be a girl or a boy and that is always and only a 1/2 probability (ignoring any biological weighting that girls may represent 51% of births or whatever the reality is).
