Lesson 11 Multiplication Strategies on Ungridded Rectangles

    • Let’s use different strategies to find the area of ungridded rectangles.

Warm-up Which One Doesn’t Belong: Multiplication in Many Forms

Which one doesn’t belong?

  1. Diagram. Rectangle split into 2 parts. One part partitioned into 3 rows of 2 of the same size squares, the other partitioned into 3 rows of 4 of the same size squares.
  2. Rectangle split into two parts. One part labeled 6 with horizontal side 2, the other labeled 12 with horizontal side 4.
  3. Addition. Three times 2 plus three times 4.
  4. Array. 3 rows of 6 dots.

Activity 1 Mark, then Express

For each rectangle:

  • Mark or shade each rectangle to show a strategy for finding its area.

  • Write one or more expressions that can represent how you find the area.

  1. Rectangle. Horizontal side 9, vertical side 5.
  2. Rectangle. Horizontal side 6, vertical side 6.
  3. Diagram. Rectangle. Horizontal side, 8 yards. Vertical side, 7 yards.

Activity 2 Card Sort: Different Expressions, Same Rectangle

Your teacher will give you a set of cards with expressions that represent areas of rectangles.

Sort the expressions into groups so that the expressions in each group can represent the area of the same rectangle. Be prepared to explain your reasoning.

You can draw rectangles if you find them helpful.

Practice Problem

Problem 1

Mark or shade the rectangle to show a strategy for finding its area. Then, explain how to use the diagram to find the area.