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This Notice and Wonder asks students to consider 2 diagrams representing a shaded region with the same side lengths. The first diagram shows the unit square and the grid lines and the second diagram just shows the side lengths of the shaded region. This prepares students to transition from the gridded diagrams they have worked with in previous lessons to the diagrams they will work with in this lesson. In the Activity Synthesis, students discuss different equations that represent different ways of finding the area.
What do you notice? What do you wonder?
The purpose of this activity is for students to find the area of rectangles with fractional side lengths where the scaffold of an area diagram is not provided. For the first product, the subdivision of each side into unit fractions is shown and then that is taken away. Without these divisions, students can either try to sketch them or use their understanding of how the numerator and denominator of the fractions relate to:
When students find products of fractions without an area diagram for support, they rely on their understanding of the meaning of the numerator and denominator and the patterns they have repeatedly observed when finding these products with area diagrams (MP8).
How did you decide whether or not to draw a diagram? How did the diagrams help you find the products?
Diego drew this diagram to represent the product . How can the diagram help Diego find the value of ? Explain or show your reasoning.
The purpose of this activity is for students to find missing values in equations that represent products of fractions. The numbers are complex so students will rely on their understanding of products of fractions rather than on drawing a diagram.
Find the value that makes each equation true. Draw a diagram if it is helpful.
“Today we found the area of rectangles without a grid and we found products of fractions without referring to any area.”
“What do you know about multiplying fractions?” (It is kind of like multiplying whole numbers, but different. We can use some of the strategies we use to multiply whole numbers. We can draw diagrams to represent equations. The numerator of the product represents the number of pieces and the denominator of the product represents the number of pieces in the whole.)
“How do diagrams represent products of fractions?” (They show that the product of the numerators is the total number of pieces shaded and the product of the denominators is the size of the pieces that are shaded.)
Display a diagram that shows .
“This diagram represents .”
“We can see that there are shaded rectangles, and rectangles in the whole. So ...”
Display:
“This always works. When we multiply fractions, we multiply the numerators and the denominators to find the product.”