3-Digit Addition and Subtraction
Lessons in this chapter
About 3-Digit Addition and Subtraction
Together and Apart - 1 repeats the structure of 1st grade double-digit work with a third column, and the extra column is where regrouping gets genuinely harder.
Add 3-Digit Numbers Without Regrouping and Subtract 3-Digit Numbers Without Regrouping re-establish the column method with the new width before any trading is involved, which is the same sequencing that worked a year earlier.
Add 3-Digit Numbers With Regrouping introduces carrying that can happen twice in one sum, and carrying from the tens into the hundreds. A child who understood carrying as a rule about the ones column has to generalise it here, which is the real test of whether the idea landed.
Subtract 3-Digit Numbers With Regrouping is the hardest lesson in 2nd grade, because of borrowing across a zero. Taking 1 from the tens column when it holds a zero means going to the hundreds first, and this is where most 2nd grade arithmetic errors live.
Solve Word Problems on Addition and on Subtraction of 3-Digit Numbers finish by putting the methods into context, where the child has to pick the operation instead of being told it.
The chapter's six lessons are six worksheets, worked in the page and marked as your child answers. Add 3-Digit Numbers With Regrouping, Subtract 3-Digit Numbers With Regrouping and Solve Word Problems on Addition of 3-Digit Numbers carry most of the practice, because regrouping across three columns is where the errors are. All of it is free to practice online.
Frequently asked questions
Adding 3-digit numbers without regrouping and then with it, subtracting them in the same order, and then word problems on each operation. The sequence is deliberate: the method is settled before the carrying and borrowing is added, and the contexts come last. It sits in Number and Operations in Base Ten (2.NBT), with the word problems reaching into Operations and Algebraic Thinking (2.OA).
Borrowing across a zero. In 403 − 157 the tens column has nothing to lend, so you have to take from the hundreds first. It is the single most common source of errors at this level.
Same method, one more column, but regrouping can now happen twice in one sum and can cross from tens into hundreds. That generalisation is what makes it harder.
So the layout is secure before the trading arrives. It is the same sequencing used in 1st grade, for the same reason.
Squared paper, one digit per square. Most column errors at this age are alignment errors rather than arithmetic ones, and the paper fixes them without any explanation.
When a column totals ten or more, the ten moves into the next column left. With three columns it can happen in the ones and again in the tens within the same sum.