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Curriculum › Math ›Grade 3

Grade 3 Math · Level 5, Measurement, Data, Area & Geometry

Find Area of Rectilinear Composite Figures

How the lesson starts: Find Area of Rectilinear Composite Figures

  1. The treehouse deck

    Hammer time! Ava and Jin are building a treehouse deck. But it's not a plain rectangle. It's shaped like a big letter L! How much floor will it have? Let's find its area.

  2. Split into rectangles

    Here's the deck. Cut it into two rectangles. The blue part is 4 rows of 2. That's 8 square units. The yellow part left over is 1 row of 4. That's 4 more. Add them: 8 + 4 = 12!

  3. Just add the parts

    Ava's porch is an L-shape split into two rectangles. One part has area 12 square units. The other part has area 8 square units. The whole porch is both parts together, so add: 12 + 8 = 20 square units! Don't subtract.