Can your young mathematician add and subtract two 4-digit numbers without regrouping? That's exactly what they do here. Subtraction is the opposite operation of addition and vice versa. Students use this relationship and their understanding of basic addition and subtraction facts to add and subtract two 4-digit numbers without regrouping in this 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.