Learning goals: Teacher Facing Determine what information is needed to solve a problem involving sales tax and discounts. Ask questions to elicit that information. Explain (orally) how to calculate the percentage, given the dollar amounts before and after a sales tax, tip, or discount. Interpret (orally and in writing) tape diagrams that represent situations involving a sales tax, tip, or discount. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 7.4 Proportional Relationships and Percentages, Grade 7.