In the previous topic, by counting, we obtained an area of 15cm2 for a 5cm by 3cm rectangle.
Notice also that 5 × 3 = 15
Thus, the area of a rectangle = “length or width” × “height”

Area = w × h
Where w is the width
Where h is the height
If Area is given then to find h or w, we use the following formula:
Area = w × h
width, w = \( \frac{Area}{h} \)
height, h = \( \frac{Area}{w} \)
Example 1:
Calculate the area of a rectangle of length 50cm and 30cm in width.
Solution:
Area = width × height
= 30cm × 50cm
= 150cm2
Example 2:
The area of a rectangle carpet is 20m2. Find the length of the shorter side in metres if the length of the longer side is 4000mm.
Solution:

First, we have to convert 4000mm to m (millimetres to metres)
1000mm = 1m
So 4000mm = \( \frac{1}{1000} \: \times \: \scriptsize 4000 \\ = \frac{4000}{1000} \\ = \scriptsize 4m\)
If A = w × h
height h = \( \frac{Area}{w} \\ = \frac{20m^2}{4m} \\ = \scriptsize 5m \)
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