## CHAPTER 6: ADDITION AND SUBTRACTION

**Lesson 8: Exploring Subtraction Strategies**

**Goal**

Subtract 3-digit numbers using personal strategies.

**Instructions for Use**

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 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.

Tic-Tac-Toe Squares — Subtraction has you answer subtraction problems involving 3-digit numbers to mark squares on a tic-tac-toe board. Use personal strategies to answer the problems.

Choose a subtraction problem on the tic-tac-toe board to answer, and type your answer in the box below the problem. Click “Go” beside your answer to check the answer, then click “Continue” to see which spot the computer marks off. Trying to make a line of three Xs, continue choosing other subtraction problems on the board to answer.