Math Focus 3
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## CHAPTER 6: ADDITION AND SUBTRACTION

### Lesson 9: Subtracting from 3-Digit Numbers

Goal

Subtract from 3-digit numbers using base ten blocks and pencil and paper.

Instructions for Use

Subtraction of 3-Digit Numbers asks you to enter 3-digit numbers, regroup them if needed, and subtract them.

Enter any 3-digit number in the first white box at the right side of the screen, then press “Enter.” Enter a smaller 3-digit number in the second white box, then press “Enter” again. Look at the columns to see if any regrouping is needed (if there is a smaller number in the top row). If so, click “Regroup” to regroup the blocks. Keep clicking “Regroup” until no more regrouping is needed. Then click “Subtract” to see the answer. Click “New Problem” to enter a new set of numbers into the boxes.

Base Blocks Subtraction has you act out subtraction problems by moving and regrouping base ten blocks.

At the bottom right of the screen, set the number of columns to 3 by clicking on the down arrow. Read the subtraction problem on the right side of the screen, then move red blocks overtop of blue blocks to subtract (delete) the blocks. To break sets of 10 or 100 into smaller blocks, such as 1s and 10s, click and drag the blocks into the next column to the right. You may also click on the screen to draw a box around single base ten blocks to regroup them into sets of 10, or draw a box around 10 sets of 10s to make sets of 100. After regrouping, move the sets into the appropriate columns and the correct answer will below the subtraction problem at the right side of the screen. After the answer appears, click “Next Problem” to continue.