The Double Decker Bus: Early Addition and Subtractionis one of eight units in the Contexts for Learning Mathematics' Investigating Number Sense, Addition, and Subtraction (K-3) This unit begins with the story of a double-decker bus-a bus that has two decks with ten seats on each. Five seats on each deck are red and five seats are white. The bus goes by quickly and the little girl in the story, sitting at her bedroom window and...