As part of an introductory activity, the students beginning a summer math class were asked to tell how many brothers and sisters they had. Tom and Harry discovered they are both from families with four children. Tom has two sisters and one brother, while Harry has three sisters.

Tom said that it is most common for families with four children to have two boys and two girls, just like his family. His reasoning is that there is a 50% chance that each child will be a boy (or will be a girl), so there must be a 50% chance that a four-child family will have 2 boys and 2 girls.

Harry argued that it is more common for a four-child family to have either three boys and one girl, or three girls and one boy. His reasoning is that, besides Tom's family, every one of the four-children families he knows of, including his own, do not have an equal number of boys and girls.

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• Which of the two boys expressed the better reasoning?
  
  
  
  
• What is the probability of a four-child family having two boys and two girls?
  
  
  
  
• What questions might be helpful in guiding a discourse when using this problem with students?