What does p(b/a) = 0.50 mean in terms of the venn diagram?

of the 4 people that have a sister,  2 of them have a brother

Step-by-step explanation:

probability of B given A

given that the person has a sister, what is the probability they have a brother

P (B/A) = 1/2

with this venn diagram

of the 4 people that have a sister,  2 of them have a brother

explanation:

previous steps have made pa≅ pb ≅ st ≅ su. setting the compass width to ab allows you to make tu the same length. then δstu ≅ δpab by the sss congruence postulate, and ∠p ≅ ∠s by the reason cpctc.