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3rd grade math · Unit 2: Lines, shapes, area, and perimeter

The cut is not perimeter

What this lesson shows

Fixes a mistake

The inside cut is not on the edge. Walk only the outside.

The worked example

The lesson works this one step by step: 6 by 8 and 4 by 5, side by side. Then your kid tries one like it on paper.

The steps

  1. Walk only the outside
  2. Six sides for an L
  3. Leave out the cut
  4. Answer in feet

Helping at home

Trace the outside edge with a finger and add only those sides, six for an L. The cut inside the shape is not part of the perimeter. Answer in feet.

If your kid gets stuck

Trace the outside edge first.

Watch it with Lux

With Lux, this lesson is a narrated video and a printed page your kid works on. Then Lux helps with the same math on their own worksheet, one question at a time.

See how Lux works

Standards

  • Common Core 3.MD.D.8
    Solve real world and mathematical problems involving perimeters of polygons, including finding the perimeter given the side lengths, finding an unknown side length, and exhibiting rectangles with the same perimeter and different areas or with the same area and different perimeters.
Matches standards in 50 statesSee each state's code

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