# National Council of Teachers of Mathematics

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National Council of Teachers of Mathematics
Moving from Additive to Multiplicative Thinking: The Road to Proportional Reasoning National Council of Teachers of Mathematics April 15, 2011 Melissa Hedges, MathematicsTeaching Specialist, MTSD Beth Schefelker, Mathematics Teaching Specialist, MPS Connie Laughlin, Mathematics Instructor, UW-Milwaukee The Milwaukee Mathematics Partnership (MMP), an initiative of the Milwaukee Partnership Academy (MPA), is supported with funding by the National Science Foundation.

Root Beer or Cola? During dinner at a local restaurant, the five people sitting at Table A and the ten people sitting at Table B ordered the drinks shown below. Later, the waitress was heard referring to one of the groups as the “root beer drinkers.” To which table was she referring? Table A Table B

How are your thoughts alike and how are they different?

Two Perspectives on Thinking
Absolute Thinking (additive) Comparing the actual number of root beer bottles from Table A to Table B. How might an additive thinker answer which is the root beer table? How might they justify their reasoning? Relative (multiplicative) Comparing amount of root beers to the total amount of beverages for each table. How might a relative thinker respond to this task? Table A Table B

Learning Intention and Success Criteria
We are learning to… develop an awareness of proportional situations in every day life. By the end of the session you will be able to…recognize the difference between additive thinking (absolute) and multiplicative thinking (relative) in student work.

Which family has more girls?
The Jones Family (GBGBB) The King Family (GBBG)

Thinking about “more” from an absolute and relative perspective
After you’ve read turn and talk: How would an additive thinker interpret “more” in this context? How would a relative thinker interpret “more” in this context? In what way will questioning strategies surfacing relative thinking?

Surfacing relative (multiplicative) thinking…
Keeping the relative amount of boys to girls the same, what would happen if… The Jones Family grew to 50? The King family grew to 40?

What happens when… Keeping the ratios of boys to girls the same….
The Jones Family grew to 100? The King family grew to 100?

Which is a better deal? M&M’s were featured in the weekly advertisement from two different stores. Greenwall’s Drug: 2 – 16 oz packages of M & M’s \$ 3.00. Drekmeier Pharmacy: 3 – 16 oz packages of M & M’s \$ 4.00. Which store offered a better deal?

Proportional Reasoning
Proportional reasoning has been referred to as the capstone of the elementary curriculum and the cornerstone of algebra and beyond. It begins with the ability to understand multiplicative relationships, distinguishing them from relationships that are additive. Van de Walle,J. (2009). Elementary and middle school teaching developmentally. Boston, MA: Pearson Education. 11

Proportional Reasoning vs Proportions
Proportional reasoning goes well beyond the notion of setting up a proportion to solve a problem—it is a way of reasoning about multiplicative situations. In fact, proportional reasoning, like equivalence is considered a unifying theme in mathematics.

What is a ratio? An ordered pair of numbers that express a multiplicative (relative) comparison. Types of ratios Part-to-Part: number of girls to number of boys Part-to-Whole: number of girls to number of children in the family

What is a proportion? A proportion is a statement of equality between two ratios. Jones Family 2:5 = 20:50 = 40:100 King Family 2:4 = 20:40 = 50:100 What do these proportions represent? Question raises ideas about part-whole, part-part relationships. If need be you could explore the proportional relationships for the Jone family.

Big Ideas of Fractions as Ratios
A ratio is a multiplicative comparison of quantities. Different types of comparisons can be represented as ratios. Ratios give the relative sizes of the quantities being compared, not necessarily the actual sizes.

CCSS Grade 6 – Narrative Ratios and Proportional Relationships
1. Students use reasoning about multiplication and division to solve ratio and rate problems about quantities. By viewing equivalent ratios and rates as deriving from, and extending, pairs of rows (or columns) in the multiplication table, and by analyzing simple drawings that indicate the relative size of quantities, students connect their understanding of multiplication and division with ratios and rates. Thus students expand the scope of problems for which they can use multiplication and division to solve problems, and they connect ratios and fractions. Students solve a wide variety of problems involving ratios and rates.

MPS Students Benchmark 3 – Grade 7 CR Item
From a shipment of 500 batteries, a sample of 25 was selected at random and tested. If 2 batteries in the sample were found to be defective, how many defective batteries would be expected in the entire shipment?

Ratio and Proportion What’s the difference?
Ratio and proportion do not develop in isolation. They are part of an individual’s multiplicative conceptual field, which includes other concepts such as multiplication, division, and rational numbers. Lo, J., & Watanabe, T. (1997). Developing ratio and proportional schemes: A story of a fifth grader. Journal for Research in Mathematics Education, 28,

Proportional Reasoning
Proportional reasoning has been referred to as the capstone of the elementary curriculum and the cornerstone of algebra and beyond. It begins with the ability to understand multiplicative relationships, distinguishing them from relationships that are additive. Van de Walle,J. (2009). Elementary and middle school teaching developmentally. Boston, MA: Pearson Education.

Thank You for coming! Melissa Hedges melissahedges@mtsd.k12.wi.us
Connie Laughlin Beth Schefelker

Milwaukee Mathematics Partnership