Task your little mathematicians to crack the code of adding hundredths and thousandths with regrouping with this fun worksheet. When adding decimals on this worksheet, students align the decimal points and use zero as a placeholder. They must also regroup the numbers to determine the sum. In each problem, the numbers are laid out in the horizontal format. Students should try to use different strategies involving composing and decomposing numbers to solve these problems. This will help them develop flexibility and fluency.