This worksheet invites students to add and subtract 1-digit numbers within 20, which helps them become proficient in addition and subtraction. The opposite operation to addition is subtraction and vice versa. In this worksheet, students apply this relationship and their knowledge of basic addition and subtraction facts to add and subtract 1-digit numbers within 20. In this worksheet, students practice solving problems written in the horizontal format. How numbers are laid out in a problem affects the method a student employs to solve it. Therefore to develop actual fluency and mastery of multiple strategies, students must practice different formats.