Amber Cline-Rabah

35 Pages·2013·2.91 MB·English

Amber Cline-Rabah
Have you ever asked yourself…
 Why is the predominant strategy for solving
proportional relationships
cross-multiplication?
 Why does cross-multiplying work?
 When students cross-multiply, what
mathematical thinking are they doing?
Solve proportional reasoning problems.
1.
Examine solution strategies and student
2.
misconceptions.
Use several sense-making strategies for
3.
solving proportional problems.
Explain the difference between algorithms
4.
and sense-making strategies.

Leave with something useful (hopefully! )
5.
Apply the mathematical practices
1.
MP.1 Make sense of problems and
persevere in solving them
MP.2 Reason abstractly and
quantitatively
MP.4 Model with mathematics
MP.7 Look for and make use of
structure
MP.8 Look for and express regularity
in repeated reasoning
we can identify at least three different
1.
strategies for solving proportional
reasoning problems.
we can explain why each strategy makes
2.
sense.
we can evaluate each strategy’s usefulness
3.
in a given situation.
we wonder why we ever taught kids to
4.
cross-multiply!
Facilitate discussion of problems and
1.
strategies and ask probing questions.
 Why is the predominant strategy for solving
proportional relationships
cross-multiplication?
 Why does cross-multiplying work?
 When students cross-multiply, what
mathematical thinking are they doing?
 A truck traveled 75 miles in 1.5 hours. At the
same rate, how long would it take the truck
to drive 325 miles?
Daniel and Katya are walking partners who
walk at the same rate. Since Daniel was
running late on Tuesday, Katya started
walking without him. By the time Daniel
arrived, Katya had already completed three
laps. How many laps will Daniel have
completed when Katya finishes her
tenth lap?
 How did you solve each problem?
 How are these questions alike?
 How are they different?
 What kind of reasoning is used in each
problem?