Answer:
4 years old
Step-by-step explanation:
His sister is x years old.
Gary is 1 year less than 3 times her age, so his age is
3x - 1
His age is 11, so we can write an equation.
3x - 1 = 11
Add 1 to both sides.
3x = 12
Divide both sides by 3.
x = 4
Answer: She is 4 years old.
