standard_description: Use informal arguments to establish facts about the angle sum and exterior angle of triangles, about the angles created when parallel lines are cut by a transversal, and the angle-angle criterion for similarity of triangles. For example, arrange three copies of the same triangle so that the sum of the three angles appears to form a line, and give an argument in terms of transversals why this is so.
problem_activity: Activity
This activity allows students to practice using the algorithm from earlier to solve division problems that involve a wider variety of fractions. Students can use any method of reasoning and are not expected to use the algorithm. As they encounter problems with less-friendly numbers, however, they notice that it becomes more challenging to use diagrams or other concrete strategies, and more efficient to use the algorithm. As they work through the activity, students choose their method.
Monitor the strategies students use and identify those with different strategies— including those who may not have used the algorithm—so they can share later.
Launch
Keep students in groups of 2. Give students 5–7 minutes of quiet work time, followed by 2–3 minutes to discuss their responses with a partner.
Representation: Internalize Comprehension.
Activate or supply background knowledge. Provide students with access to blank tape diagrams. Encourage students to attempt more than one strategy for at least one of the problems.
Supports accessibility for: Visual-spatial processing; Organization
Student Facing
Calculate each quotient. Show your thinking and be prepared to explain your reasoning.
\(\frac 89 \div 4\)
\(\frac 34 \div \frac 12\)
\(3 \frac13 \div \frac29\)
\(\frac92 \div \frac 38\)
\(6 \frac 25 \div 3\)
After biking
\(5 \frac 12\)
miles, Jada has traveled
\(\frac 23\)
of the length of her trip. How long (in miles) is the entire length of her trip? Write an equation to represent the situation, and then find the answer.
Student Response
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Student Facing
Are you ready for more?
Suppose you have a pint of grape juice and a pint of milk. You pour 1 tablespoon of the grape juice into the milk and mix it up. Then you pour 1 tablespoon of this mixture back into the grape juice. Which liquid is more contaminated?
Student Response
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for free access to Extension Student Response.
Activity Synthesis
Select previously identified students to share their responses. Sequence their presentations so that students with the more concrete strategies (e.g., drawing pictures) share before those with more abstract strategies. Students using the algorithm should share last. Find opportunities to connect the different methods. For example, point out where the multiplication by a denominator and division by a numerator are visible in a tape diagram.
Conversing, Representing: MLR7 Compare and Connect.
As students consider the different strategies, invite them to make connections between the various representations and approaches. Ask, “What do each of the strategies have in common?”, “How are the strategies different?” and “Which strategy is more efficient? Why?” Listen for and amplify observations that include mathematical language and reasoning.
Design Principle(s): Maximize meta-awareness; Optimize output (for comparison)


aligns: no