Perimeter of Rectangle, Square & Triangles Basic 3 Mathematics Lesson Note

A. COUNTING SKILL: NUMBERS 861-880

Counting from 861 to 880: 861, 862, 863, 864, 865, 866, 867, 868, 869, 870, 871, 872, 873, 874, 875, 876, 877, 878, 879, 880

Practice counting:

• From 865 to 875: _______
• From 872 to 880: _______
• Backwards from 880 to 870: _______

Fill in missing numbers:

• 866, 867, _____, 869, _____
• 875, _____, 877, _____, 879
• _____, 862, _____, 864, _____

B. WRITING SKILL: WRITING OF THE NUMBERS

Write in words:

• 861 = Eight hundred and sixty-one
• 865 = Eight hundred and sixty-five
• 870 = Eight hundred and seventy
• 875 = Eight hundred and seventy-five
• 880 = Eight hundred and eighty

Write in figures:

• Eight hundred and sixty-three = _______
• Eight hundred and sixty-eight = _______
• Eight hundred and seventy-two = _______
• Eight hundred and seventy-seven = _______
• Eight hundred and seventy-nine = _______

C. WHAT IS PERIMETER?

Definition: Perimeter is the distance around the outside of a shape.

How to find perimeter: Add up all the sides of the shape.

Example: A triangle has sides 3cm, 4cm, and 5cm. Perimeter = 3cm + 4cm + 5cm = 12cm

D. PERIMETER OF RECTANGLES

Rectangle properties:

• 4 sides
• Opposite sides are equal
• 2 long sides (length)
• 2 short sides (width)

Formula for rectangle perimeter: Perimeter = length + width + length + width Or: Perimeter = 2 × length + 2 × width

Example: Rectangle: length = 6cm, width = 4cm Perimeter = 6 + 4 + 6 + 4 = 20cm Or: Perimeter = 2 × 6 + 2 × 4 = 12 + 8 = 20cm

Practice:

1. Rectangle: length = 8cm, width = 3cm Perimeter = _____ + _____ + _____ + _____ = _____ cm
2. Rectangle: length = 5cm, width = 2cm Perimeter = _____ cm
3. Rectangle: length = 10cm, width = 4cm Perimeter = _____ cm

E. PERIMETER OF SQUARES

Square properties:

• 4 sides
• All sides are equal

Formula for square perimeter: Perimeter = side + side + side + side Or: Perimeter = 4 × side

Example: Square with side = 5cm Perimeter = 5 + 5 + 5 + 5 = 20cm Or: Perimeter = 4 × 5 = 20cm

Practice:

1. Square: side = 6cm Perimeter = 4 × _____ = _____ cm
2. Square: side = 3cm Perimeter = _____ cm
3. Square: side = 8cm Perimeter = _____ cm
4. Square: side = 7cm Perimeter = _____ cm

F. PERIMETER OF TRIANGLES

Triangle properties:

• 3 sides
• Sides can be different lengths

Formula for triangle perimeter: Perimeter = side 1 + side 2 + side 3

Example: Triangle with sides 4cm, 6cm, 8cm Perimeter = 4 + 6 + 8 = 18cm

Practice:

1. Triangle: sides = 3cm, 4cm, 5cm Perimeter = _____ + _____ + _____ = _____ cm
2. Triangle: sides = 6cm, 7cm, 8cm Perimeter = _____ cm
3. Triangle: sides = 5cm, 5cm, 6cm Perimeter = _____ cm
4. Triangle: sides = 2cm, 3cm, 4cm Perimeter = _____ cm

G. PERIMETER OF REGULAR SHAPES

Regular shapes: All sides are equal length.

Examples:

• Regular triangle: 3 equal sides
• Square: 4 equal sides
• Regular pentagon: 5 equal sides

Formula for regular shapes: Perimeter = number of sides × length of one side

Examples:

1. Regular triangle: side = 4cm Perimeter = 3 × 4 = 12cm
2. Regular pentagon: side = 6cm Perimeter = 5 × 6 = 30cm

Practice:

1. Regular triangle: side = 7cm Perimeter = 3 × _____ = _____ cm
2. Regular hexagon (6 sides): side = 5cm Perimeter = 6 × _____ = _____ cm

H. QUANTITATIVE REASONING

Word problems:

1. A rectangular garden is 12m long and 8m wide. What is the perimeter of the garden?
2. A square playground has sides of 15m each. How much fencing is needed to go around it?
3. A triangular field has sides measuring 20m, 25m, and 30m. What is the perimeter?
4. Kemi walks around a rectangular field that is 50m long and 30m wide. How far does she walk?

Comparison problems:

1. Which has a larger perimeter?
   1. Square with side 8cm OR Rectangle 10cm × 5cm?
2. A triangle with sides 6cm, 8cm, 10cm OR a square with side 6cm?

Pattern recognition:

1. Square perimeters: side 1cm = 4cm, side 2cm = 8cm, side 3cm = _____, side 4cm = _____
2. Rectangle 5cm × 2cm = 14cm, 5cm × 3cm = 16cm, 5cm × 4cm = _____, 5cm × 5cm = _____

Real-life applications:

1. A farmer wants to fence a rectangular farm 40m × 25m. How much fencing does he need?
2. A picture frame is 20cm long and 15cm wide. What is the perimeter of the frame?
3. A school compound is square-shaped with each side 80m. How far is it to walk all around the compound?

CLASS EXERCISES

1. Count from 868 to 878:
2. Write in words:
   1. 867 = _______
   2. 873 = _______
   3. 880 = _______
3. Find perimeter of rectangles:
   1. Length 9cm, width 4cm: Perimeter = _____ cm
   2. Length 12cm, width 5cm: Perimeter = _____ cm
4. Find perimeter of squares:
   1. Side 6cm: Perimeter = _____ cm
   2. Side 9cm: Perimeter = _____ cm
5. Find perimeter of triangles:
   1. Sides 4cm, 5cm, 6cm: Perimeter = _____ cm
   2. Sides 7cm, 8cm, 9cm: Perimeter = _____ cm
6. Regular shapes:
   1. Regular triangle, side 8cm: Perimeter = _____ cm
   2. Regular pentagon, side 4cm: Perimeter = _____ cm
7. Word problems:
   1. A rectangular book is 25cm long and 18cm wide. What is its perimeter?
   2. A square tile has sides of 12cm. What is the perimeter?
   3. A triangle has sides 9cm, 12cm, and 15cm. Find the perimeter.
8. Compare perimeters:
   1. Square with side 7cm OR Rectangle 8cm × 6cm?
   2. Which has the bigger perimeter?
9. Missing measurements:
   1. Rectangle perimeter = 24cm, length = 8cm. Width = _____ cm
   2. Square perimeter = 28cm. Side = _____ cm
10. Problem solving: A school playground is rectangular, 60m long and 40m wide. Students run around it 3 times. How far do they run in total?