Mathematics 3

# Surf for More Math

## Lesson 7 - Subtracting 2-Digit Numbers

To encourage students to have fun on the Web while learning about Subtracting 2-Digit Numbers, here are some games and interactive activities they can do on their own or in pairs.

### Goal

Subtract 2-digit numbers with and without regrouping.

### Builds Upon

Student Book pages 94-96

### Instructions for Use

Subtracting 2-Digit Numbers provides students with strategies to mentally subtract 2-digit numbers.

To find the difference of the two numbers, click the 'Start Subtraction' button. Input the answer in the text box next to the 'Check' button, then click 'Check'. See if the answer is correct. Continue to find the difference of the next two numbers.

The Subtraction Machine lets students practice subtracting 1-digit and 2-digit numbers.

To use The Subtraction Machine, choose a skill level, type the answer in the text field, and click the red button to check it.

Base Block Subtraction lets students practice subtraction with and without regrouping.

To use Base Block Subtraction, drag a base block into a column to the left. If students move a block one column to the right, it breaks apart to show the exchange, for example, a 10-long for ten units. To group pieces to exchange the other direction, click and hold the mouse key down while dragging a rectangle to "lasso" the pieces. The newly grouped object can then be dragged into the next column.

To complete a preset subtraction problem, select base 10 and click on the 'Next Problem' button. Move any pieces and drag them into the next column to ungroup. Click, hold, and drag the mouse to move blue blocks on top of red blocks of the same size to cancel each other out. Blocks will disappear also, if a red block is placed on top of a blue block of the same size. Start with the 1s column and work to the 1000s column. The subtraction solution will appear on the left.

To subtract the blocks to create your own problem, click on the 'Create Problem' button and then use the blue blocks at the top to enter blocks above the dashed line. Click on the red blocks at the top to enter blocks below the dashed line. As long as students has two numbers correctly represented in the specified base, the subtraction problem will appear on the left. To solve it, click on the 'Begin Problem' button and move the blue blocks on top of the red blocks of the same size. Start with the 1s column and work to the 1000s column. The subtraction solution will appear on the left.