Perimeter for 4th Grade
Perimeter is the distance around a shape. For fourth graders, finding perimeter usually means adding the lengths of all the sides of a polygon. For a rectangle, we can add the four sides, or use the formula: perimeter = 2 × length + 2 × width (or 2 × (length + width)). For a square, we multiply one side length by 4.
Perimeter is measured in linear units: inches, feet, yards, centimeters, or meters. Real-world uses include putting a fence around a yard, framing a picture, or running around the edge of a field. Understanding perimeter helps students connect math to everyday situations.
DETAILED EXPLANATION
To find the perimeter of any polygon, add the lengths of every side. If some sides are equal (like in a rectangle or square), we can use shortcuts. For a rectangle with length L and width W, the perimeter is 2L + 2W because there are two lengths and two widths. For a square with side s, the perimeter is 4s.
Sometimes not all side lengths are given. If we know a rectangle has one side of 7 cm and another of 4 cm, we know the opposite sides are the same, so the perimeter is 7 + 4 + 7 + 4 = 22 cm, or 2 × (7 + 4) = 22 cm.
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WORKED EXAMPLES WITH STEP BY STEP SOLUTIONS
Example 1
A rectangle has length 12 meters and width 8 meters. Find the perimeter.
Solutions:
Step 1: A rectangle has two lengths and two widths. So we add: 12 + 12 + 8 + 8.
Step 2: 12 + 12 = 24 and 8 + 8 = 16. So 24 + 16 = 40 meters.
Alternatively: Perimeter = 2 × (length + width) = 2 × (12 + 8) = 2 × 20 = 40 meters.
Answer: 40 meters
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Example 2
A square has a side length of 9 centimeters. What is its perimeter?
Solutions:
Step 1: A square has four equal sides. So perimeter = 4 × side length.
Step 2: 4 × 9 = 36.
Answer: 36 centimeters
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