Logic Puzzle

Sally has 3 brothers, meaning there are 3 boys in the family besides Sally. Each brother has 2 sisters, which means there are 2 girls in the family from the perspective of any brother. Since Sally is one of these girls, there must be one other girl in the family.

Therefore, Sally has one sister.

This can be verified by considering the family composition:

• Girls: Sally and one other sister (let's call her Anna).
• Boys: Three brothers.

From Sally's perspective:

• She has 3 brothers (the three boys).
• She has 1 sister (Anna).

From the perspective of any brother:

• They have 2 sisters (Sally and Anna).

The conditions are satisfied: Sally has 3 brothers, and each brother has 2 sisters. If there were only one girl (Sally), each brother would have only one sister, which contradicts the given information. If there were three girls, each brother would have three sisters, which also contradicts the given information. Thus, there must be exactly two girls in the family.

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