Which of these two women is more likely to be the parent of two girls? Explain.
Professor Robertson and Professor Simpson are both mathematicians. Professor Robertson tells you that she has exactly two children, at least one of whom is a girl. Then Professor Simpson tells you she has exactly two children also, and that the older one is a girl, but says nothing about the gender of they younger child. Which of these women is more likely to be the parent of two girls? Explain.