The purpose of this lesson is twofold: to start familiarizing students with the idea of interest, and to show several examples that illustrate the difference between applying a percentage change to a new quantity and applying to the original quantity. Both activities present problems without providing much scaffolding, offering an opportunity for students to make sense of the problem and persevere in solving (MP1). When students explain why they agree or disagree with a character’s statement, they are justifying their reasoning and critiquing the reasoning of others (MP3).