Slug (identifier)
perimeter-elementary
Equivalent file in the opposite grade group
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Title (level 2)
3rd and 4th grade
Title slug (identifier)
third-and-fourth-grade
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Corps
Perimeter is the measurement of the contour or outline of a plane figure or surface.
Example:
The perimeter of the figure corresponds to the measurement of the orange line.
Title
How do we calculate the perimeter?
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The perimeter of a figure is obtained by adding all the side measurements.
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When calculating the perimeter, make sure that only one unit of measurement is used. If not, convert the units before doing the calculations.
Example:
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What is the perimeter of this figure?
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I check that the same unit of measurement is used. If not, I must convert it.
To learn how, see the concept sheet Converting Units for Measuring Length.
Since the other units are in cm, I convert 1 dm to cm.
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I add the lengths of all the figure’s sides to find the perimeter.
5 cm + 5 cm + 10 cm + 5 cm + 15 cm + 10 cm = 50 cm
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The perimeter is 50 cm.
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How do we find a missing measurement when the perimeter is known?
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To find the missing measurement of a plane figure from a given perimeter, a subtraction is required.
To find out how to find a missing term in an addition, see the concept sheet Finding a Missing Term in an Addition.
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Find the missing measurement in this figure.
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I know I have to add the side measurements to find the perimeter.
10 mm + 20 mm + 30 mm + 20 mm + ? mm + 40 mm + 60 mm + 40 mm = 240 mm
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I subtract the known side measurements from the perimeter to find the missing side.
240 mm - 10 mm - 20 mm - 30 mm - 20 mm - 40 mm - 60 mm - 40 mm = 20 mm
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The missing side measurement of the perimeter is 20 mm.
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Links
Title
Finding a Missing Term in an Addition
Title
Units for Measuring Length
Title
Converting Units for Measuring Length
