Grace's age is 3/8th the age of her grandmother. Her grandmother is twice the age of Grace's mother. If Grace's mother is 80 years old, how old is Grace? Let's think first. Chain of thought:
Grace's grandmother is 2 * 80 years = 160 years old. Grace's age is 3 / 8 * 160 years = 60 years old.
Therefore, the answer is 60.