Students commonly discover the need to regroup numbers as they add multi-digit numbers. They divide each ten into 10 ones, each hundred into 10 tens, and so on. Use add 4-digit and 3-digit numbers with regrouping worksheet to give your students practice with this concept. 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.