Interactive tools on this page:

Here are 5 interactive projector tools for adding and subtracting designed to be used in small group discussion or on a projector.

1. Add to 20
2. Add to 10, 20, 100 or a random number
3. Number line for addition and subtraction
4. Singapore math add to 20 bar
5. Singapore math add to 100 bar

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Adding/subtracting to 10, 20 or 100

GeoGebra link

GeoGebra link

Number Line

Change

• the max to 20 or to 100 for addition/subtraction to 20 or 100.
• the min to a negative number if students are ready for negative numbers.

 

 

GeoGebra link

Number chat suggestions:

1.  Click all three red objects to show all three numbers and make ‘addition’ or ‘subtraction’ sentences with all three numbers.
2. Click on two of the three red objects to show two numbers and ask students to calculate the third value.
3. Give a value for the red line, and ask students to come up with a start and the end that will give the red line value.

 

Number Bar 20

This number bar has a maximum value of 20. Like the number line above, the diagram is drawn to scale to allow students to develop their sense of number alongside their sense of space.

GeoGebra link

Here is a zero to 20 number line from Math Salamanders.

Number bar 100

Here is a number line to 100 from Math Salamanders.

GeoGebra link

Look for and celebrate a diversity of approaches, including approaches that are mathematically correct even if the student ended up with the wrong answer.

Notice if student answers are in the right ‘ballpark’, even if they are not fully accurate. If students are using spatial sense alone they may not get the correct number but are still nonetheless engaged in productive mathematizing.

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