A number of people are stopped at random in the street. They are asked if they have two children and also if one of them is a boy born on a Friday. Someone answers yes to both questions. What is the probability that this person has two boys? (Equal chance of giving birth to a boy or girl and of giving birth on any day).

Answer: 13/27

Hi!

How do I solve this question? Preferably with probability formulas.

Thank you!