Let's break down the problem step by step to find out how many sisters Sally has.

Problem Statement: Sally has 3 brothers. Each brother has 2 sisters. How many sisters does Sally have?

Understanding the Relationships:

1. Sally's Brothers:

   • Sally has 3 brothers.

2. Brothers' Sisters:

   • Each brother has 2 sisters.

Analyzing the Information:

• Since Sally is a girl, she is one of the sisters that her brothers have.

• Let's denote the number of sisters Sally has as S.

Setting Up the Equation:

• Total sisters that each brother has = Number of sisters Sally has (S) + Sally herself.

  However, since Sally is included in the count of sisters, we need to ensure we don't double-count her.

Calculating the Number of Sisters:

1. From Sally's Perspective:

   • Sally has S sisters.

2. From Each Brother's Perspective:

   • Each brother has 2 sisters.
   • These 2 sisters include Sally and her sisters.

Relating Both Perspectives:

• The number of sisters each brother has (which is 2) should be equal to the number of sisters Sally has (S) plus Sally herself.

  Therefore:

  [ S + 1 = 2 ]

  Here, S + 1 accounts for Sally and her sisters.

Solving for S:

[ S + 1 = 2 \ S = 2 - 1 \ S = 1 ]

Conclusion:

Sally has 1 sister.

Verification:

• Sally has 3 brothers.

• Each brother has 2 sisters: Sally and her 1 sister.

  This satisfies the condition that each brother has 2 sisters.

Final Answer:

Sally has 1 sister.