standard_description: Use coordinates to prove simple geometric theorems algebraically. For example, prove or disprove that a figure defined by four given points in the coordinate plane is a rectangle; prove or disprove that the point (1, Ö3) lies on the circle centered at the origin and containing the point (0, 2).
problem_activity: Narrative
In this activity, students solve problems that involve finding multiples that are shared by two different numbers: the number of hot dogs in a package and the number of hot dog buns in a package. They reason about how many of each package to get to make a certain number of servings of hot dogs. As multiple answers can be expected, the focus is on explaining why the solutions make sense (MP3).
To solve the problems, students may decontextualize the situation and reason about factors and multiples, and then recontextualize the solutions in terms of servings of hot dogs. As they do so, they practice reasoning quantitatively and abstractly (MP2). During the synthesis, analyze different solutions and discuss why numbers that are multiples both of 8 and 10 are useful in this situation.
Launch
Groups of 2–4
Read the opening paragraph as a class.
“What questions could you ask about the situation?”
1 minute: quiet think time
Share responses.
“Let’s solve problems about hot dogs and hot dog buns, which come in different-size packages.”
“For each problem, look for possible numbers of packages that are needed to serve hot dogs at a picnic.”
“Take a minute to read the problems and think about how you would solve them.”
1 minute: quiet think time
Activity
“Now work with your group to solve these problems.”
8–10 minutes: group work time
Monitor for students who:
use the term “multiple” in their explanations
try different possibilities for the number of packages to buy
try to find numbers of packages that would give the exact (or close to the exact) numbers of servings
Student Facing
Each package of hot dogs has 10 hot dogs. Each package of hot dog buns has 8 buns.
Lin expects to need 50 hot dogs for a class picnic.
How many packages of hot dogs should Lin get? Explain or show your reasoning.
Can Lin get exactly 50 hot dog buns? How many packages of hot dog buns should Lin get? Explain or show your reasoning.
Diego expects to need 72 hot dogs for a class picnic.
How many packages of hot dogs should Diego get? Explain or show your reasoning.
How many packages of hot dog buns should Diego get? Explain or show your reasoning.
Is it possible to buy exactly the same number of hot dogs and buns? If you think so, what would that number be? If not, explain your reasoning.
Student Response
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Advancing Student Thinking
If students are using guess and check, consider asking: “How are you choosing which numbers to try?” or “How can thinking about multiples help you solve the problem?”
Activity Synthesis
Invite students to share their responses to the problem about 72 hot dogs, including those who get 70 hot dogs and 72 buns or 80 hot dogs and 80 buns. Encourage students to highlight how they are using multiples in their reasoning.
“Why are there different answers to this question?” (The numbers do not work out exactly to get 72 hot dogs and 72 buns, so we need to look at different alternatives.)
“Is it possible to buy exactly the same number of hot dogs and buns? If so, how many of each?” (Yes, 40, 80.)
“Why is it possible to buy exactly the same number of hot dogs and buns when the packaging is different?” (Some multiples of 10 are also multiples of 8, such as 40 and 80.)


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