Mathematics 3

# Surf for More Math

## Lesson 7 – Subtracting from 3-Digit Numbers

To encourage your child to have fun on the Web while learning about Subtracting from 3-Digit Numbers, here are some games and interactive activities they can do on their own or in pairs.

Goal
Subtract from 3-digit numbers using pencil and paper.

Builds Upon
Student Book pages 156-157

### Instructions for Use

Base Block Subtraction lets your child practice subtraction with and without regrouping.

To use Base Block Subtraction, drag a base block into a column to the left. If your child moves 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 your child 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.

Subtracting 3-Digit Numbers prompts your child to practice subtraction with and without regrouping.

To use Subtracting 3-Digit Numbers, select from the pull-down menus the number of questions and the amount of time to complete them. Click the ‘Start’ button. Drag-and-drop number disks into the holes before time runs out. Press the ‘Next’ button to begin a new question.

Vertical Subtraction lets your child practice subtraction from 3-digit numbers.

To use Vertical Subtraction, have your child input the answers in the text fields. At each text field, the user is prompted by a question. Input the answer and press ‘Check’ after each question. When your child has completed the questions, click the ‘Next’ button to add a different question.