Percent Increase and Decrease (Discount Mark-Up Tax) Math LibMath lib activities are a class favorite! In this activity, students will practice solving problems related to discount, mark-up, sales tax, tip, percent increase, and percent decrease as they move through 10 stations. The answers they get will generate a funny story about their teacher. This is a much more fun approach to multiple choice, and the students adore reading the story to the class. They get very excited to see which of thei