In this worksheet, students find the missing number using the count-on method or the relationship between addition and subtraction. To solve add 2-digit and 1-digit numbers with regrouping worksheet, they must also regroup the numbers. 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.