Three-digit addition exercises that require regrouping, which means adding numbers that are carried over from one place to another. How to do this worksheet 1. Add the ones digit first. If the sum is greater than 9, carry the tens digit to the next place. Go to the tens digit. 2. Add the tens digit plus the carried value from the ones digit. If the sum is greater than 9, carry the value to the hundreds digit. Finally, the hundreds digit. 3. Add the hundreds digit plus the carried value from the