Learning goals: Teacher Facing Comprehend “sales tax” and “tip” as two contexts that involve adding a percentage of the initial amount. Explain (orally) how to calculate the total cost including a tax or tip, given the “subtotal” and the percentage. Explain (orally) how to determine the percentage of the subtotal that a tax or tip is. Full lesson plan (warm-up, activities, synthesis, cool-down prompt) from 7.4 Proportional Relationships and Percentages, Grade 7.