Teaching Models

Subtracting Three-Digit Numbers

Extending the skill of subtracting two-digit numbers to three-digit numbers is begun by subtracting multiples of 100, such as 700 − 500, which can be viewed as 7 hundreds − 5 hundreds = 2 hundreds.

Next, subtraction with regrouping tens or hundreds is introduced. The procedure illustrated by using base-ten blocks is then extended to the subtraction algorithm through the use of a place-value chart. The subtraction algorithm consists of subtracting the ones, then the tens, and then the hundreds, regrouping when necessary.

When a horizontal subtraction problem is presented to children, be sure to emphasize the need to correctly align the digits before completing the subtraction.

Place-Value Chart and Subtraction Algorithm

Adding and Subtracting Money
When adding and subtracting money at this grade level, children are shown that the addition or subtraction is completed as if whole numbers are involved. Then the dollar sign and decimal point are placed in the answer.


Teaching Model 22.4: Check Subtraction


Houghton Mifflin Math Grade 2