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  • 4th Grade
  • Math
  • About 10 minutes

Find the Missing Side

Use the area or the perimeter to find the missing side.

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Find the Missing SideName:Date:Use the area or the perimeter to find the missing side.Area = 21 sq ft3 ftPerimeter = 38 yd9 ydArea = 40 sq ft4 ftPerimeter = 30 cm7 cmPerimeter = 26 in4 inArea = 30 sq ft3 ftk5printables.com · Sheet #146124601 · Aligned with Common Core 4.MD.A.3

This is sheet #146124601.

How to do it

  1. Read the area or perimeter.
  2. Work backward to find the missing side.
  3. Write it in the box.

Teaching tip

Check the answer by putting it back into the formula. This sheet is aligned with Common Core 4.MD.A.3.

Find the Missing Side worksheet for 4th grade (area and perimeter), free printable
Printable preview

About this worksheet

Rectangles with one missing side to find from the area or perimeter. Fewer uses area only.

What kids practice

Perimeter is the distance around a shape, and area is the space inside it. Fourth graders use formulas for rectangles. Perimeter is P = 2 × l + 2 × w, or 4 × s for a square. Area is A = l × w, measured in square units. They also work backward to find a missing side, like a rug with an area of 48 square feet and a width of 6 feet, which is 8 feet long.

Watch for

  • Mixing up area and perimeter, especially in word problems.
  • Adding only two sides for perimeter, like 8 + 5 = 13 instead of 26.
  • Writing perimeter in square units or area in plain units.
  • Dividing the perimeter by 4 to find the length of a rectangle that is not a square.

It's free to print, with Fewer, Standard or More on the page and an answer key. See the full area and perimeter guide for 4th grade.

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