Week 3 – Jss 1 Third Term Mathematics Lesson Notes

WEEK 3.
TOPIC: AREA AND PERIMETER OF PLANE SHAPES
PERIMETER: The perimeter of a plane shape is the length of its outside boundary. This means the distance round its edges.
Examples
1. The length of a rectangular room is 5m and the width is 4m. find the perimeter of the room
Solution
The length of the room = 5m
The width of the room = 4m
Perimeter = 2(l+w)
Perimeter = 2(5+4)
Perimeter = 2(9)= 2×9= 18m

1. The perimeter of a square is 2580cm. find the length of the square in meter.

Solution:
P= 2580cm = 25.8m
P= 4 x length = 4l
L = 25.8/4
L = 6.45m
Therefore, the length of the square = 6.45m

1. Calculate the perimeter of a triangle with dimensions 4.2m, 3.6m and 5.7m.

Solution:
Perimeter = (4.2 + 3.6 + 5.7) meters
Perimeter = 13.5m

1. A parallelogram has sides measuring 200mm by 150mm. what would be the length of the side of a square having the same perimeter?

Solution
Length of parallelogram = 200mm
The width of the parallelogram = 150mm
Perimeter = 2( L + w)
Perimeter = 2(200 + 150) mm
Perimeter = 2 x 350 = 700mm
But
Perimeter of the square = 4 x length = 4L
4L = 700mm
Divide both sides by the coefficient of l
L = 700/4 = 175
Therefore length of the square = 175mm

1. Calculate the perimeter of a circle of diameter 14cm.

NOTE: The perimeter of a circle is called circumference and the diameter (D) is twice the radius (r). thus D = 2r
Solution:
Method 1: circumference = πd

C = 22/7 x 14
C = 44cm
Method 2:
R = D/2 = 14/2 = 7cm
C = 2 x 22/7 x 7
C= 44cm

 AREA: Area of shapes is the measure of amount of surface it covers or occupies.
Examples :

1. Calculate the area of rectangular room with dimension 250cm by 200cm.

Solution:
A = (250 x 200) square cm
A =50 000 cm square.

1. Find the area of a square of sides 14cm.

Solution:
A = 14 x 14
A = 196 cm square

1. Evaluate the area of a parallelogram with base 8cm and height 9cm.

Solution:

A = 8 X 9
A = 72 cm square

1. Calculate the area of a trapezium with parallel sides 10cm and 18cm and height 12cm.

Solution:
Area =
Area = ½ (10 + 18) x 12
Area = ½ (28) x 12
Area = 14 x 12
Area = 168 cm square.

 Do these
Exercise 18.2 pg 198 No (2, 3,4 & 5)
Exercise 18.3 pg 200 No (2, 3, 4 & 5)

  Assignment
Exercise 18.6 pg 209 No (2, 4, 5,9 & 10)