Missing Numbers: Addition and Subtraction to 20 Mixed Numbers Math Worksheets K–5 worksheets help students build number sense by finding the unknown in addition and subtraction equations — a key foundational skill for early math learners. Each page features 12 carefully designed problems with a clean, kid-friendly layout that keeps students focused and engaged. Blank boxes guide students to identify whether the missing number is a first addend, second addend, sum, minuend, subtrahend, or differe