If Mandy is 3 years old, then her brother is 3 * 4 = 12 years old.
And her sister is 12 - 5 = 7 years old.
The age difference between Mandy and her sister is 7 - 3 = 4 years.
#### 4
The answer is: 4
Below is a math problem. Provide a detailed, step-by-step solution.

### Problem:
If Mandy is 3 years old and her brother is 4 times as old as she is, and her sister is 5 years younger than her brother, what is the age difference between Mandy and her sister?

### Answer:
