"You are an engineer who wants to build different kinds of bridges. The bridges will be made of colored rods. The first bridge you are to build is a 1-span bridge made with one yellow rod and two red rods." (Build the bridge illustrated below, with the students copying.) "The yellow rod is called a span, and the red rods are called supports . Since the yellow rod is 5 cm long, the length of the bridge is 5 cm."

"The second bridge you are to build is a 2-span bridge made with two yellow rods and four red rods (as shown below). Note that this bridge is 10 cm long."

"As you build bridges in the following activities, think of a way to keep track of the number of rods of different colors you use. Your goal is to find out how many rods of each color you would need to build a bridge of any size."

Student assessment activity: Distribute the activity sheet and read through question 1 to be sure that the children understand the basic problem. Note: the bridges have been scaled to fit the 7" × 10" page of this volume. The teacher may choose to redraw the bridges to scale when they are reproduced on standard size paper



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