Category: Math Aids

Composing and Decomposing Numbers with Glass Gems


Composing and Decomposing Numbers with Glass Gems is a first-grade math activity designed for Occupational Therapists to do with their patients to exercise fine motor skills and meet common core standards like composing and decomposing numbers. This shows that number can be built in many ways, but if the child takes away a specific amount of gems (or subtracts), there is only one number that can "fit" in that corner of the triangle.  Likewise, if they subtract either number from a composed triangle statement, they will always get the other corner's number (assuming the math has been done correctly).

Technical Specifications: 

Step One: Gather materials.

  • 1 pound of clear glass gems
  • Permanent marker
  • Paper

Step Two: Draw triangles with the marker on the paper.

Step Three: Write two numbers in two corners of the triangles.

Step Four (optional): The child can use the gems as counting manipulatives or add the two numbers up by counting the glass gems.

To learn how to compose a number:

Step Five: The child writes the total in the empty corner of the triangle. This adding numbers together, or building a number is called composing a number. Another way to say composing numbers is to think about putting numbers together.

Then, to learn the concept of decomposing numbers:

Step Six: Draw another triangle and start with a higher number and a lower number. The child can use the clear glass gems to subtract by counting out the manipulatives. This taking apart of a number is called decomposing a number.  Another way to say decomposing numbers is to say "taking apart" a number.

Then, write out the addition and subtraction sentences using boxes with the composed and decomposed numbers.


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Composing and Decomposing Numbers with Glass Gems

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