Strategic

Question: A girl went to school, and her teacher asked her how old she was. Girl: I don't know, but I know I'm half my mother's age Teacher: how old is your mother Girl: I don't know, but she is 5 years younger than my dad Teacher: how old is your dad Girl: I don't know, but if you add all our ages, they count up to 100. How old is the girl, mother, and dad?