Adding Three-Digit Numbers

Extending the skill of adding two-digit numbers to three-digit numbers is begun by adding multiples of 100, such as 300 + 600, which can be viewed as 3 hundreds + 6 hundreds = 9 hundreds.

Next, addition with regrouping ones or tens is introduced. The procedure illustrated by using base-ten blocks is then extended to the addition algorithm through the use of a place-value chart. The addition algorithm consists of adding the ones, then the tens, and then the hundreds, regrouping any sum greater than 9 in each place.

Teaching Model 21.2: Regroup Ones