# Modeling Addition and Subtraction of Two-Digit Numbers

Students use an online application to model the addition and subtraction of up to two-digit numbers that may require grouping or ungrouping. Students may record their work for the addition application and the subtraction application on the recording sheets that can be downloaded using the links below. Questions for debriefing may be found on the webpage.

Addition: Students use an online application to model the addition of up to two-digit numbers that may require grouping . Students may record their work on the recording sheet that can be downloaded using the link below. The teacher or parent may wish to work the first problem with the students to demonstrate the process.

1. Click on the ADD button to start.
2. Move the cows from the top two areas down to the sum area to combine the cows.
3. If there are cows that are not in a corral, determine if they can be grouped by 10s. To group the 10 cows click on the GROUP button, then click on the 10 cows that need to be groups, and then click on the GROUP button again.
4. Determine the sum of the cows and click on the CHECK button. Click on the numbers to enter the number of cows and click on the green check mark.
5. Click on ANY Numbers to be given a number sentence or click on MY Numbers to enter a number sentence.

Subraction: Students use an online application to model the subraction of up to two-digit numbers that may require grouping. Students may record their work on the recording sheet that can be downloaded using the link below. The teacher or parent may wish to work the first problem with the students to demonstrate the process.

1. Click on the SUBTRACT button to start.
2. Move the nubmer of cows to be subtracted from the top area down to the lower left hand area.
3. If there are not enough cows that are loose to subtract, ungroup a corral of 10 cows. To ungroup the 10 cows click on the UNGROUP button, and then click on the 10 cows that need to be ungrouped.
4. Determine the difference and click on the CHECK button. Click on the numbers to enter the number of cows and click on the green check mark.
5. Click on ANY Numbers to be given a number sentence or click on MY Numbers to enter a number sentence.

Click this button to visit the Grouping and Grazing game:

Grouping and Grazing

After students have completed a few problems, debrief with the questions found on the webpage by clicking on the plus sign next to the word "Exploration".