Can your young mathematician add and subtract thousandths less than 1? That's exactly what they do here. When adding or subtracting decimals, students line up the decimal points and add extra zeros to the right of the number so that each decimal has the same number of digits. Students then add or subtract digits at each place to find the answer. This worksheet is about practicing with the horizontal format in which numbers are written side by side. To develop flexibility with numbers and operations, students need to have enough practice in this format and not just rely on the vertical/column method.