Review with students the concept of ratio (“a comparison of numbers based on division”) and some examples of ratios. Ask them to watch for how ratios are used by the professional in Futures Channel Movie #4013, Designing Toy Cars. Once the movie is over, ask them to work in pairs or small groups to solve a problem such as this (working in pairs or small groups): I am making a scale model of a car. The actual car is 120 inches long, and my model is 12 inches long. If the actual car is 60 inches high, how high should my model be? Coach individual groups with questions and comments such as these: Compare the length of the actual car and model car by division. What is the ratio? (120/12 or 10/1). Do you think the heights of the actual car and model should compare in the same way? (Yes). Why? Otherwise the model wont’ have the same shape.What would the height of the model car have to be so that the ratio of heights is 10/1? (6 inches)
Discuss with the class the fact that the two ratios (the lengths ratio and the heights ratio) have to be equal to each other for your model to look right, and task for other examples of situations where ratios have to be the same. (Maps, other scale models, drawings that are supposed to look like real objects). Explain that a proportion is a statement that two ratios are equal (such as length actual car/length model = height actual car/height model) and that in this chapter they will be learning more about how to work with proportions in many situations. |
