Figure this out.

A girl went to school and her teacher asked her ''How old are you?''
Gil replied :''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 I know my dad is 5 years older than my mum''
Teacher: ''How old is your dad?''
Girl: ''I don't know but I know that if we add our ages the answer is 100years''

Now how old is the girl,her mum and her dad?

Any good guess? :-)