Students demonstrate their problem-solving ability as they work on this add two 6-digit numbers without regrouping worksheet. Students use the count on strategy or the relationship between addition and subtraction to find the missing number in this worksheet. However, they do not need to regroup numbers to get to the answer in add two 6-digit numbers without regrouping worksheet. 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.