Definition
Bar model
A bar model uses rectangular bars to show quantities and how they are related.
What it means
Turn the quantities into bars so the structure of the problem is visible. A whole bar can be split into parts, two bars can be lined up for comparison, or repeated equal sections can show groups. The bars organize the information; they do not choose the calculation for you.
Remember it
Build the story with bars before choosing the operation.
Example
A class collected 18 cans on Monday and 7 fewer on Tuesday. Draw a Monday bar labelled 18 and a shorter Tuesday bar with a missing part of 7. The aligned bars show 18 − 7 = 11 cans on Tuesday.
Watch for
A decorative rectangle is not a bar model; the bars and labels must encode the quantities and their relationship.
Common mix-up
A bar model can support many operations, so its shape alone does not tell you to add or subtract.
Exact meaning
A bar model is a diagram in which rectangular bars, segments, and labels represent quantities and relationships such as part–whole, comparison, equal groups, ratio, or an unknown value. Bar lengths must be used consistently for the intended relationship.