Janet is three years older than her sister julie. janets brother is eight years younger than their sister julie. the sum of all of their ages is 55 years

If Janet = Julie + 3

Janet Bro = Julie - 8

and Janet + Janet Bro + Julie = 55

Janet is 23.

Julie is 20.

Janet's brother is 13.

Let's name Janet's age x

julie is then x-3 years old

and the brother is x-3-8=x-11

and all three of them: x+x-3+x-11 are 55

so we count:

2x-3+x-11=55

3x-3-11=55

3x-14=55

add 14 5o both sides:

3x=69

divide by 3:

x=23

so Janet is 23, Julie is 23-3=20 and the brother is 20-8=12 years old!