Scale Drawing On Length and Height JSS2 Mathematics Lesson Note

 SCALE DRAWING

Since it is not always possible to draw on paper the actual size of real-life objects such as the real size of a car, or an airplane, we need scale drawings to represent the size like the one you see below of a van.

 In real life, the length of this van may measure 240 inches. However, the length of a copy or print paper that you could use to draw this van is a little bit less than 12 inches

Since 240/12 = 20, you will need about 20 sheets of copy paper to draw the length of the actual size of the van

To use just one sheet, you could then use 1 inch on your drawing to represent 20 inches on the real-life object

You can write this situation as 1:20 or 1/20 or 1 to 20

Notice that the first number always refers to the length of the drawing on paper and the second number refers to the length of a real-life object

Example #1:

Suppose a problem tells you that the length of a vehicle is drawn to scale. The scale of the drawing is 1:20

If the length of the drawing of the vehicle on paper is 12 inches, how long is the vehicle in real life?

Set up a proportion that will look like this:

Do a cross-product by multiplying the numerator of one fraction by the denominator of the other fraction

We get :

Length of drawing × 20 = Real length × 1

Since the length of the drawing = 12, we get:

12 × 20 = Real length × 1

240 inches = Real length

Example #2:

The scale drawing of this tree is 1:500

If the height of the tree on paper is 20 inches, what is the height of the tree in real life?

Set up a proportion like this:

Do a cross-product by multiplying the numerator of one fraction by the denominator of the other fraction

We get :

Height of drawing × 500 = Real height × 1

Since the height of the drawing = 20, we get:

20 × 500 = Real length × 1

10000 inches = Real height