It is common for students to regroup numbers when they add multi-digit numbers. They understand that one hundred is ten tens, one ten is ten ones, and so forth. Use add 3-digit and 1-digit numbers with regrouping worksheet to help your students practice this concept and develop their conceptual and strategic knowledge. 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.