A part-part-whole model represents a quantity as a whole made from two parts, showing that the parts combine to make the whole and that either part can be determined when the other two quantities are known. Within 20, this structure connects addition equations with related subtraction equations and supports composing and decomposing numbers while distinguishing the total from an individual part; multi-part, larger-number, and generalized algebraic treatments are outside this scope.
A part-part-whole model shows how two parts join to make one whole.
Example:
There are crayons. are red. How many are blue?
First, find the whole and the known part:
Draw the model:
To find the missing part, subtract the known part from the whole:
So, there are blue crayons.
The model also shows the related addition fact:
The two parts, and , combine to make the whole, .
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