Answer:
One chance in two
Step-by-step explanation:
A parent can only have one or the other meaning a son or daughter. Both the son and the daughter represent one half of a probability of having each one separately. On whether or not the parent will have a daughter as the eighth child, is completely irrelevant as a parent can only bare a son and daughter. This would mean they would have a one chance in two for either cases, but due to the context of the question, it would be for the daughter. So therefore, they would have one chance in two.
Thank you,
Eddie