Calculating Area from Scale Drawings: Ratios and Proportions

This video tutorial teaches how to calculate actual areas from scale drawings using ratios and proportions. It explains proportions, common mistakes in setting up ratios, and the effect of scale factors on area. The tutorial uses algebra to demonstrate how squaring the scale factor of sides gives the scale factor of areas. Finally, it applies these concepts to calculate the material needed for making school flags.

What is a proportion?

• An equation that relates two unequal ratios

• A technique to find the area of a rectangle

• A method to solve equations using addition

• An equation that relates two equal ratios

What happens to the area of a rectangle if its side lengths are doubled?

• The area remains the same

• The area triples

• The area doubles

• The area quadruples

How do you find the ratio of areas for similar figures?

• By adding the side lengths

• By squaring the scale factor of the side lengths

• By multiplying the side lengths

• By subtracting the side lengths

If the original flag is 40 inches wide and 30 inches tall, what is the ratio of heights for a 4-inch tall replica?

• 10 to 1

• 8 to 1

• 15 to 2

• 5 to 1

How much material is needed to make 420 small flags if each small flag has an area of 21 and one third inches squared?

• 9,500 square inches

• 8,960 square inches

• 9,000 square inches

• 8,500 square inches