Can you calculate a tip or a discount in your head? Help your students build these real-world mental math skills, by reasoning about percents. In this lesson students will practice finding 10, 5, 20 and 15 percent using mental math reasoning related to the 10% benchmark. Full lesson plan, includes variations for students who already have a percent calculation procedure and those who don't; and activities to build application skills or algebraic thinking. Includes: Lesson plan, with 3 variatio