Who doesn't know this from their daily teaching practice? As soon as your students are allowed to use calculators, basic mental arithmetic skills become obsolete. For even the simplest calculations, they quickly reach for the calculator. However, mental math is not only essential in school but also in everyday life and the professional world. With the exercises in the following volume covering all important curriculum topics for grades 9 and 10, your students will become proficient in working with numbers again: Each page features two sets of problems that you can use as handouts, OHP transparencies, or easily as flashcards. Detailed solutions on the back of each sheet allow for collective or individual checking. Numerous tips and tricks for effective mental math round out the offering. The topics: Percentage calculations.