4.5 D) Area of Rectangles – Part 1
We are able to find the area of a rectangle by multiplying the length by the width.
What is the area of the rectangle below? Each of the squares on the grid equate to 1 square cm (1 cm2).
We are able to work out the area of this rectangle by multiplying the length by the width. The rectangle has been drawn on squared paper and this makes it easier to find the length and the width. The length of the rectangle is 5 cm and the width of the rectangle is 3 cm.
We can now work out the area of the rectangle.
Therefore, the area of the rectangle is 15 cm2.
We could have worked out the area of the rectangle by counting the number of 1 cm2 squares that there are inside the rectangle. When we count the number of 1 cm2 squares inside the rectangle, we see that there are 15, thus meaning that the area of the rectangle is 15 cm2.
This example is quite nice because we are able to work out the area in two different ways. However, it is rare that you will be given a question in the exam whereby you can work out the area by counting squares. Usually you will be finding the area of a rectangle by multiplying the length by the width.
What is the area of the rectangle below?
We work out the area of a rectangle by multiplying the length by the width. The length for the above rectangle is 3 m and the width of the above rectangle is 7 m. We can sub these values into the area formula.
The area of the rectangle is 21 m2.
The rectangle below has an area of 30 cm2. Find the length of y?
We can work out the length of y by using the area of a rectangle formula. The formula is given below:
The question tells us that the area of the rectangle is 30 cm2, the length of the rectangle is y and the width of the rectangle is 5 cm. We can sub these values into the area of a rectangle formula and simplify.
We want to find the value of y and not 5y. Therefore, we need to divide both sides of the equation by 5.
The unknown side is 6 cm.