standard_description: Understand subtraction as an unknown-addend problem. For example, subtract 10 – 8 by finding the number that makes 10 when added to 8.
problem_activity: Stage 2: Multiple Rectangles
Required Preparation
Materials to Gather
Folders
Grid paper
Inch tiles
Materials to Copy
Blackline Masters
Can You Build It Stage 2 Directions
Number Cards (0-10)

Narrative
Before playing, students remove the cards that show 6 or higher and set them aside.
Students flip two number cards to get a number of tiles and then each partner tries to create as many rectangles as possible for that area. If both students each found all the rectangles, they get one point. A student gets two points for any rectangle they built that their partner did not. The player who gets the most points after eight rounds is the winner. Students may choose to draw their rectangle on grid paper, rather than use inch tiles.
This center stage is the first time Number Cards 0–10 are used in Grade 4, so they are provided as a blackline master. Students will continue to use these throughout the year. Consider copying them on cardstock or laminating them and keeping them organized to be used repeatedly.
Additional Information
Each group of 2 needs at least 120 inch tiles and a set of number cards.


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