To know the final probability that this has happened, we must multiply the probability of each event, they tell us that the probability that it is a girl is 1/2 and this happened 4 times, therefore:
(1/2) ^ 4 = 0.0625
that is, the probability that 4 girls are born is 6.25%
an unusual probability is considered when it is less than 5%, therefore, although it approaches this figure, it is not unusual
