Perimeter: Find the Missing Side Worksheets for 3rd Grade
Use the perimeter and the known sides to find one missing side length. 15 free printable worksheets, each with an answer key.
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Click a worksheet to open the PDF, or grab the matching answer key. Every sheet prints on one page.
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Perimeter: Find the Missing Side: what children learn
When the perimeter and all but one side are known, the missing side is the perimeter minus the sum of the known sides. These pictures are not drawn to scale, so the numbers must be used, not a ruler.
Perimeter: Find the Missing Side: worked example
The perimeter is 24 units. Three sides are 5, 7, and 6 units. What is the missing side? 6
The known sides add up to 5 + 7 + 6 = 18. The missing side is 24 - 18 = 6 units.
Perimeter: Find the Missing Side: a common mistake to watch for
Kids sometimes write the sum of the known sides as the answer instead of subtracting it from the perimeter.
Perimeter: Find the Missing Side: how to help at home or in class
Cut a piece of yarn 20 inches long and say it makes a rectangle with one side 6 inches. Your child works out the other side, then tests it by bending the yarn into the shape and measuring. The leftover after two 6-inch sides is 8 inches, split between two equal sides. Ready when your child checks an answer by adding all four sides back to 20.
What is on these Perimeter: Find the Missing Side worksheets
This set has 15 different worksheets for 3rd grade, with 9 questions on each and a matching answer key for every sheet. The instruction printed on each worksheet is: “Use the perimeter to find the missing side.”
Every answer on every sheet is checked by a separate program before the worksheet is published. How we check answers