Problem
A circle of radius 1 cm has diameter 1 + 1 = 2 cm, so it fits inside a small 2 cm by 2 cm square cell.
The widest part of a circle is its diameter, which equals twice the radius.
3.G.A.1Draw A DiagramAlong one side, 6 cm holds 6 / 2 = 3 cells. The square is 6 cm tall too, so it holds 3 rows of cells.
Splitting a length into equal 2 cm pieces is division within 100.
3.OA.C.7Look For A PatternA 3 by 3 grid of cells holds one circle per cell, for 9 circles in total.
Equal rows and columns of objects are counted by multiplication, an array model from Grade 3.
3.OA.C.7Create A Physical RepresentationThe three-by-three grid of 2 cm cells holds exactly nine circles, one in each cell.
One circle sits in each cell with none left over, so counting the circles is the same as counting the cells.
Matching each circle to its own single cell pairs the two groups one for one, so the two counts must be equal.
The cells are laid out in three equal rows of three, so their total is three rows times three cells, which is 3 times 3.
Three equal rows of three is the same as adding three groups of three together, and that repeated adding of equal groups is exactly what multiplying counts.
Each circle needs a 2 cm box -- count the boxes across and down, then multiply, just like a Grade 3 array!