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

The side you split

What this lesson shows

Fixes a mistake

After the cut, a piece uses only part of the long side.

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. Cut it in two
  2. Not the whole side
  3. Subtract to find the part
  4. Add the areas

Helping at home

After the cut, ask which part of each long side belongs to each rectangle. Subtract to find the part that is left, then multiply each rectangle’s own sides and add.

If your kid gets stuck

Which part of the bottom is under each rectangle?

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.C.7d
    Recognize area as additive. Find areas of rectilinear figures by decomposing them into non-overlapping rectangles and adding the areas of the non-overlapping parts, applying this technique to solve real world problems.
Matches standards in 49 statesSee each state's code

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