standard_description: Add and subtract fractions with unlike denominators (including mixed numbers) by replacing given fractions with equivalent fractions in such a way as to produce an equivalent sum or difference of fractions with like denominators. For example, 2/3 + 5/4 = 8/12 + 15/12 = 23/12. (In general, a/b + c/d = (ad + bc)/bd.)
problem_activity: Narrative
The purpose of this activity is for students to find areas of rectangles where one side is a whole number and the other side is a fraction that is greater than 1.  Students should solve the problems in a way that makes sense to them. Ask students to explain how the diagrams show the multiplication expressions.
Engagement: Provide Access by Recruiting Interest.
Synthesis: Optimize meaning and value. Invite students to share how they use the diagram to calculate the area of the desk or the garden and the method they used to do so with a classmate.
Supports accessibility for: Conceptual Processing, Attention
Launch
Groups of 2
Activity
5 minutes: individual work time
5 minutes: partner work time
Student Facing
Write a multiplication expression to represent the area of the shaded region.
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What is the area of the shaded region?
Write a multiplication expression to represent the area of the shaded region.
[IMG]
What is the area of the shaded region?
Student Response
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Advancing Student Thinking
If students do not write multiplication expressions to represent the area of the shaded region, prompt them to explain how they found the area of the shaded region. Then, write expressions to represent the student’s strategy and ask, “How do these expressions represent your strategy?”
Activity Synthesis
Ask several students to share their responses to the second problem.
Display:
\(3 \times 3\frac{3}{4}\)
\(3 \times \frac{15}{4}\)
“How do these expressions represent the area of the shaded region?” (They are the width and length of the shaded region. In one, the length is a whole number and some fourths, and in the other, it is all fourths.)
“How is finding the value of these two expressions different?” (For the first one, I can multiply 3 by 3 and then 3 by
\(\frac{3}{4}\)
and add them together. For the second one, I can see how many fourths I have using multiplication.)


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