Logic Puzzle

Let's break down the problem:

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

Let's analyze:

Sally's siblings:

• 3 brothers (let's call them B1, B2, B3)
• Sally herself

The brothers' sisters:

• Each brother has 2 sisters.

Who are the possible sisters for each brother?

• Sally is a sister to each brother.
• Are there any other sisters? That's the question!

If Sally is the only girl, then each brother would only have 1 sister (Sally). But the problem says each brother has 2 sisters.

Therefore, there must be another sister besides Sally.

Let's check: Suppose Sally has 1 sister (besides herself). So the siblings are:

• Sally (girl)
• A second sister (let's call her Anna)
• 3 brothers

Children in the family:

• 2 girls (Sally and Anna)
• 3 boys (the brothers)

Now, for each brother:

• Their sisters are Sally and Anna: 2 sisters (matches the problem statement).

So, Sally has 1 sister.

Final answer:

[ oxed{1} ]

Sally has 1 sister.