Logic Puzzle

This is an interesting logical reasoning problem! Let's work through it step by step.

We know:

• Sally is a girl
• Sally has 3 brothers
• Each brother has 2 sisters

The key insight is that Sally herself counts as a sister to her brothers. So when we're told that "each brother has 2 sisters," Sally is one of those sisters.

Since each brother has 2 sisters total, and Sally is one of them, that means each brother has 1 sister besides Sally.

But all brothers share the same sisters (they're all siblings in the same family). So if Sally has 3 brothers, and each brother has the same 2 sisters (Sally and someone else), then Sally has exactly 1 sister.

Therefore, Sally has 1 sister.