options: Number & Operations - Fractions: students learn to understand fractions as numbers and may work with them using addition, subtraction, multiplication, and division.

Counting & Cardinality: students learn to know number names and the count sequence, count to tell the number of objects, and compare numbers.

Ratios & Proportional Relationships: students learn to recognize, describe, represent, and reason with ratios, rates, proportional relationships, and percent.

Functions: students learn to define, use, and evaluate functions to model relationships between quantities.

Number & Operations in Base Ten: students learn to work with the base-ten system and build place value understanding.

Number Systems and Quantity: students learn to understand the complex number system and reason quantitatively.

Statistics & Probability: students learn to analyze and produce data distributions, and build understanding of univariate and bivariate data. They learn to interpret data, make statistical inferences, justify conclusions, understand rules of probability, and use probability to make decisions.

Measurement & Data: students learn to work with data and measure attributes such as time, money, length, area, and volume. They may learn to compare measurements to operations and convert between different units of measure.

Operations & Algebra: students learn to solve problems using algebraic thinking and operations such as addition, subtraction, multiplication, and division. They may learn to identify and explain arithmetic patterns, evaluate or manipulate numerical expressions, and reason with equations and inequalities.

Geometry: students learn to classify geometric figures by their properties, and understand and compare the relationships between them. Students develop and use formulas to compute lengths, areas, and volumes, and they use transformations to generate new shapes and compare existing ones. Geometry can be studied with and without coordinates.

Modeling: students learn to choose and use appropriate mathematics and statistics to analyze real-world empirical situations, improve decisions, and report on their conclusions and the reasoning behind them.
problem_activity: Narrative
In the second round of analysis and design, students use their knowledge of operations and expressions to complete a Which One Doesn’t Belong set with two missing items. Students first study the attributes of the given items. They articulate why the items all belong to a set and why each one has a reason not to belong. Next, they propose a new item that shares a feature with others in the set but also has a unique feature that excludes it from the set.
Launch
Groups of 2
5 minutes: independent work time
Activity
“Work with your partner to make sure each new item added to the set has a reason to belong and not to belong.”
5 minutes: partner work time
Student Facing
Here is an incomplete Which One Doesn’t Belong set. It has two missing items.
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Find at least one reason that the first two items, A and B, belong in the set.
Add two items to complete the set. Make sure there is at least one reason that each new item belongs and at least one reason it doesn’t belong.
C and D both belong because . . .
C doesn't belong because . . .
D doesn't belong because . . .
After you’ve completed the set, check items A and B. Does each one still have a reason not to belong? If not, adjust your new items so that A and B are each still unique in some way.
Student Response
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Activity Synthesis
Invite students to share their analyses and new items.
“Why do both A and B belong to the set?”
“What were some features of the expressions that you looked at or experimented with to complete your set?” (The kind of numbers used, how many numbers are used, the order of the numbers, the symbols, the value of the expression.)
If no students considered the value of the expression, ask them about it.
“After adding C and D, did A and B still have a reason not to belong in your set? Did you have to revise your items?”


correct_option_index: 4