Brady Bunch, The - One Plus One Equals Two
This slip up occurs between two epiosodes. In one episode, Father of the year, Marcia needs help with her math homework and she wants Mike to help her. Carol (her mother) offers to help her and Marcia rolls her eyes and refuses,saying,"But, mom, it's math homework and you know that you aren't any good with math." But then, in the episode Alice dosen't live here anymore, Alice offers to help Greg with his math homework and he shakes his head and tells her, "No thanks, mom (Carol) is a whiz at math."