Definition
Part-whole model
A part-whole model shows a whole quantity and the parts that add exactly to it.
What it means
Think of one amount taken apart without losing or adding anything. Every piece belongs to the whole, and the pieces together make exactly the total. The model lets you add the parts to find the whole, or subtract a known part from the whole to find a missing part.
Remember it
Parts join; the total stays the same.
Example
A bar for 14 is split into a part worth 9 and a part worth 5. The two parts fill the bar, so 9 + 5 = 14. If the whole 14 and the part 9 are known, the missing part is 14 − 9 = 5.
Watch for
Two groups drawn beside the number 14 are not enough. The labels and layout must show that every part belongs to, and exactly makes, the whole.
Common mix-up
The parts do not have to be equal. Equal-sized parts matter in some fraction models, but an additive part-whole model may have parts such as 9 and 5.
Exact meaning
A part-whole model is an additive representation in which one whole quantity is decomposed into two or more non-overlapping parts, and the values of those parts sum to the value of the whole.