Problem
Each square is 3 cm wide and the rectangle is 15 cm wide, so divide to find how many squares fit in one row: 5 squares.
How many equal 3 cm pieces fit in 15 cm is a division question.
3.OA.A.3Identify SubproblemsThere are 10 squares in all and 5 squares per row, so divide to find how many rows there are: 2 rows.
Total squares split into equal rows gives the number of rows.
3.OA.A.3Identify SubproblemsEach row is 3 cm tall and there are 2 rows, so multiply to get the rectangle's other side: 6 cm.
Stacking 2 squares each 3 cm tall gives a height of 6 cm.
3.OA.A.3Draw A DiagramThe rectangle's unknown side measures 6 cm.
The unknown side is rows of squares stacked up, and 2 rows each 3 cm tall make 6 cm.
The rows sit one above another with no gap or overlap, so each row's 3 cm height adds into the whole side.
Every row is the same 3 cm tall, so 2 equal rows is just 3 added twice, which is 2 times 3.
The 10 squares split evenly into rows of 5, and 10 divided by 5 is 2 rows.
Along the 15 cm width the 3 cm squares sit side by side, and 15 divided by 3 is 5 per row.
The square widths lie end to end with no gap, so five 3 cm widths rebuild the full 15 cm.
Finding how many 3s make 15 reverses multiplying 3, and division is what undoes multiplication.
The rows together hold all 10 squares with none left out, so counting how many 5s fill 10 is a division.
The rows share no squares and miss none, so the row groups add back to all 10 squares.
Asking how many 5s make 10 reverses multiplying 5, and division undoes multiplication.
The rectangle is 15 cm by 6 cm. Add the four sides, or double the sum of width and height: 42 cm.
A rectangle's perimeter is twice the length plus twice the width.
3.MD.D.8Identify SubproblemsFind the rows and columns of squares, then add up the sides: Grade 3 division and perimeter!