1. DeAnn Huinker, Melissa Hedges, Chris Guthrie, & Beth Schefelker
Multiplying & Dividing Fractions – The Challenge of Computation vs. Conceptualization
Math Alliance July 27, 2010
DeAnn Huinker, Melissa Hedges, Chris Guthrie, & Beth Schefelker

3. Learning Intentions & Success Criteria
Learning Intention – We are learning to:
Deepen our conceptual understanding of division and multiplication with fractions.
Success Criteria – You will be able to:
Use real-life problem-solving situations to surface the meaning of division and multiplication of fractions.
Goals for the MTL Content Strand
To deepen your knowledge of mathematics so that you can use this knowledge in your work with students and in your work as a Math Teacher Leader. 3

4. Popcorn Party Serving Size: 2 cups
How many servings from:
8 cups of popcorn
5 cups of popcorn

5. Summarize Is this a measurement or partitive context?
Popcorn Party: Serving Size 2 cups How many servings from 8 cups; 5 cups?
Is this a measurement or partitive context?
Write the equation for each situation (8 cups; 5 cups).
Identify the meaning of each number in the equations.
Draw a picture, make a diagram, or use paper strips to show how you got your answer.

6. Summarize How many 2–cup servings?
÷ =
cups cup servings
serving
1 2
÷ = 2
cups cup
serving
servings

7. What does the represent?
1 2
What does the represent?
One-half of a cup of popcorn?
One-half of a serving?
Are you sure?
Idea here is: ½ of a serving, but a remainder of 1 cup of popcorn.

8. Popcorn Party Serving Size: cup
1 2
How many servings from:
1 cup of popcorn
4 cups
1 2
cups

9. Summarize How many 2–cup servings?
÷ =
cup servings
÷ =
cups
1 2
cup
serving
1 2
servings
cup
serving

10. Task Popcorn Parties #1 & #2
Facilitator
Paper Strip Demonstrator

11. Algorithm

12. Task Popcorn Parties #1 & #2
Facilitator poses one problem at a time.
Each individual silently solves it.
On facilitator’s cue: State answer.
Take turns as the demonstrator who models with paper strips.
Take turns to justify your reasoning.

13. Popcorn Party #1 1 4 How many servings can be made from:
Serving Size: cup of popcorn
How many servings can be made from:
1 cup of popcorn
2 cups of popcorn
3 1/2 cups of popcorn 1 4

14. Popcorn Party #2 3 4 How many servings can be made from:
Serving Size: cup of popcorn
How many servings can be made from:
3/4 cup of popcorn
6 cups of popcorn
2 1/4 cups of popcorn
4 1/2 cups of popcorn 3 4

15. Popcorn Party Serving Size: cup
3 4
How many servings from 4 cups?
Using your paper strips, work individually to solve the problem.
THEN compare results.

16. ÷ =
cups
3 4
cup
serving
Just as with whole numbers, it is important to understand the meaning of the answer and how to interpret and relate ways of reporting “remainders.”
Think about a “leftover or extra” amount
Think about the “number of groups”
Think about the “size of a group”
Answer: 5 1/3 servings; related to 5 complete servings, 1/3 of another serving; related to 5 complete servings with a remainder of ¼ cup of popcorn.

17. Interpreting Remainders
For each problem,
Place it in a context
Solve it with paper strips
Interpret the solution with both a “leftover” and as it relates to the “groups.”
7 8
3 8
÷ = ?
5 8
3 ÷ = ?
Think about
“leftover or extra” amount
the “number of groups”
the “size of a group”

18. Discussion
In reviewing these division situations and your solutions, what are you noticing?

20. Consider ⅔ × ¾
Describe a real-world situation that can be modeled by this equation.  What could the ⅔ represent?  What could the ¾ represent? Turn and Share
As you crafted a real-world situation, what struggles emerged?

21. What insights surfaced? In what ways are 2×3 and ⅔ × ¾ similar?
Back to the basics…
Consider for a moment 2×3.  What could the 2 represent?  What could the 3 represent?
What insights surfaced?
In what ways are 2×3 and ⅔ × ¾ similar?
In what ways are they different?
Does the meaning of multiplication change when moving from whole numbers to fractions?

22. What do you understand about 2/3 x 3/4?
“Algorithms for multiplication of common fractions are easy for teachers to teach and students to use, but their meanings are elusive.”
-- Zhijun Wu

23. Julie is making the family dinner
Julie is making the family dinner. She buys 4 packages of meat for the spaghetti. Each package weighs 5/8 lb. How many pounds of meat does she buy?
Turn and talk –  What does the 4 represent?  What does the 5/8 represent?
Individually –
Work through this problem.
Record your thinking on note cards.
Represent your thinking using numbers, pictures, & words.
Place face down in the middle of your table when done.

24. Debriefing Strategies
Each person picks a card to study.
After 30 seconds pass the card to the right.
Study the strategy on each card.
After all cards have been passed, share comments, questions or ah-ha’s with the table group.
Table Discussion
How do these strategies demonstrate an understanding of multiplication?

25. Looking at student work...
Julie is making the family dinner. She buys 4 packages
of meat for the spaghetti. Each package weighs 5/8 lb. How many pounds of meat does she buy?
In what ways do the students show understanding of the situation as multiplication? How do students show that they understand the “number of groups” and the “size of groups” in their representations?

26. “These types of situations can be modeled by the repeated-addition interpretation. The link between multiplication and addition is clearly seen here. The repeated-addition model offers a satisfying interpretation in this case.”
--Zhijun Wu
How does your thinking change when you consider this next problem . . .

27. Taking a run...
I wanted to run 4 miles. I ran 5/8 of the distance before I stopped for water. How many miles did I run before I had to stop for water?
Put your pencils down. Turn and talk –  What does the 4 represent?  What does the 5/8 represent?
Individually –
Work through this problem.
Record your thinking on note cards.
Represent your thinking using numbers, pictures, & words.
Place face down in the middle of your table when done.

28. Taking a run...
Strategy Debrief 1. Each person picks a card to study. 2. After 30 seconds pass the card to the right. 3. Study the strategy on each card. 4. After all cards have been passed, share comments, questions or ah-ha’s with the table group. Table Discussion How do these strategies demonstrate an understanding of multiplication?

29. Thinking about parts and wholes
Combining parts: Problem 1 4 = packages of meat 5/8 = weight per package (quantity)‏ “4 parts of 5/8 lbs each”
Finding part of a group:
Problem 2 4 = miles OR the whole run
5/8 = part of the 4 miles (5/8 is now the operator – we do not need a complete whole but we need a part of that whole.)‏
“5/8 parts of 4 miles”

30. Taking a Run – Looking at Student Work
In what ways do the students show understanding of the situation as multiplication?

31. What does multiplication of fractions encompass?
Multiplication of fractions involves:
 Combining equal parts
 Finding a part of a whole or part of a group
Doing both – combining equal parts and finding part of a whole.
Problem Sort
Read through each problem.
As a table, decide which problem type is represented in each context.
Solve using pictures, diagrams, and numbers.

32. From Whole Numbers to Fractions
What experiences do students need to extend the meaning of multiplication from whole numbers to multiplication of fractions?
Experience with real-life problem solving situations.
Use of concrete and pictorial representations to support students as they reason.
Opportunities to explore the meaning of multiplication through a variety of problem formats involving fractions.

33. Homework
To help you prepare for the exam next week it is recommended that you complete the following:
Division of Fractions
Read Beckmann pp
Do Practice Problems for Section 7.4 pp #1, #3, #8a, b, c
Multiplication of Fractions
Read Beckmann pp
Do Practice Problems for Section 6.1 pp

34. Problems for Card Sort
Mrs. Smith has 120 books in her fourth grade classroom. 4/5 of the books are fiction. How many books are fiction?
All notebooks at the local store are discounted by ¼ A notebook originally cost $0.96. How much do you save on one notebook if you buy it today?
Julie bought 4/5 of a yard of fabric for her class project. Later she found that she needed only ¾ of the material. How much material did Julie use for her project?
At the supermarket potatoes are bagged in ¾ pound bags. Mom bought 3 bags of potatoes. How many pounds of potatoes did mom buy?
Red cabbage cost $0.39 a pound. Julie bought 3 1/3 pounds of red cabbage to prepare her dish. How much did she pay for the red cabbage?
I put a container holding a half gallon of ice cream into the freezer. Two days later the ice cream container is 2/3 full. How much ice cream is in the container?
Melissa is planning on making several batches of cookies. She needs 2/3 cup of sugar for every batch she makes. She plans on making 2 ½ batches. How much sugar will she need to make these batches.