Grade 4 Mathematics
Perimeter is the distance AROUND a shape. We ADD up all the sides.
Area is the space INSIDE a shape. We MULTIPLY length times width.
Easy to remember: Perimeter = Plus (add) | Area = Array (multiply)
OR add all 4 sides:
P = l + w + l + w
Units: cm, m, ft, in
Length times width
(rows times columns)
Units: sq cm, sq m, sq ft
Find the perimeter of this rectangle:
Method 1 - Add all sides: P = 9 + 4 + 9 + 4 = 26 cm
Method 2 - Use the formula: P = 2(9) + 2(4) = 18 + 8 = 26 cm
The perimeter is 26 cm (just centimeters, not square centimeters!)
Find the area of a rectangle that is 7 feet long and 5 feet wide:
Think: How many 1-foot squares fit inside?
Use the formula: A = length x width = 7 x 5 = 35 square feet
The area is 35 sq ft (square feet because we're measuring a 2D space!)
WRONG: A rectangle is 6 m by 4 m. Student writes: "Perimeter = 6 x 4 = 24 square meters"
RIGHT: Perimeter = 6 + 4 + 6 + 4 = 20 meters (ADD the sides, regular units)
Area = 6 x 4 = 24 square meters (MULTIPLY for area, square units)
A rectangle has a perimeter of 30 inches. The length is 9 inches. What is the width?
Write the formula: P = 2l + 2w
Plug in what you know: 30 = 2(9) + 2w
Solve: 30 = 18 + 2w, so 12 = 2w, so w = 6 inches
1. Find the perimeter and area of a rectangle with length = 10 cm and width = 6 cm.
Perimeter = cm
Area = sq cm
2. A rectangle has a perimeter of 28 meters. The width is 5 meters. What is the length?
Length = meters
3. A garden has an area of 56 square feet. The length is 8 feet. What is the width?
Width = feet
4. Maria wants to put a border around her rectangular poster. The poster is 12 inches long and 8 inches wide. How many inches of border does she need?
Answer: inches