lesson
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Imagine you have a giant chocolate bar divided into 100 mini-squares. If you have 0.65 of the bar and give your friend 0.24, how much do you have left?
Whenever we take away parts of a whole, we can see the answer right in front of us by crossing out pieces on a grid.
The Decimal Grid
In decimal operations, we use a unit transformation to redefine our blocks: a base-ten flat or full grid boundary represents one whole (1.00).
Each rod or full column represents one tenth (0.1 or 101), and each small unit cube or cell represents one hundredth (0.01 or 1001).
📊Interactive diagram
Now that we can picture tenths and hundredths, how do we subtract them?
Subtracting on a Grid
Decimal subtraction uses minuend-only modeling: shade only the minuend (0.56, the starting amount), rather than modeling both numbers.
Next, cross out what you take away: 2 full columns (2 tenths) and 3 tiny squares (3 hundredths).
📊Interactive diagram
Count whatever is left shaded without an X: 3 columns and 3 loose squares make 0.33.
What happens if you do not have enough single squares to cross out?