Problem
Divide the 30 cm width by the 5 cm side to get 6 columns of squares.
Dividing the width by one square's side length gives how many squares fit in a row — the Grade 2 idea of partitioning a length into equal pieces.
Identify Subproblems2.G.A.2Measuring LengthDivide the 20 cm height by the 5 cm side to get 4 rows of squares.
The same division idea applies to the height, giving the number of rows — just the width's reasoning carried over to the vertical side.
Identify Subproblems2.G.A.2Measuring Length6 squares in each of 4 rows multiply to 24 squares total.
The squares sit in a neat grid, so each of the 4 rows holds the same 6 squares — adding that group of 6 four times is exactly 6×4. Since the grid covers the whole sheet with no gaps or overlaps, this product is exactly the total count.
Identify Subproblems3.MD.C.7Measuring LengthThe number of 5 cm squares in the sheet equals the 6 squares in one row multiplied by the 4 rows.
The 5 cm squares sit in a neat grid, so each of the 4 rows holds the very same 6 squares, and the total is those 4 equal groups of 6.
Taking the same group of 6 squares once for every one of the 4 rows is adding 6 over and over, which is exactly what multiplying 6 by 4 means.
Adding the rows really does account for every square, because the grid covers the whole sheet with none left out and none counted twice.
When a shape is split into pieces with no gaps and no overlaps, those pieces add back to exactly the whole shape.
Cutting a rectangle into a grid of equal squares means the total count is columns multiplied by rows.