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The purpose of this Warm-up is to recall multiplication diagrams used in an earlier grade to find the product of 2 two digit numbers. This prepares students for finding the product of 2 mixed numbers in this lesson by decomposing the mixed number into a whole number and a fraction and then finding and adding partial products.
What do you notice? What do you wonder?
The purpose of this activity is for students to compare different methods to find the value of a product of mixed numbers. First, they solve problems in a way that makes sense to them. Then they compare an area diagram, which students have seen in earlier lessons, with a more abstract diagram like those students examined in the Warm-up. Then they compare both diagrams with another strategy that renames the mixed numbers as fractions, and then uses the method they generalized in previous lessons to find the product of any two fractions.
In a later unit, students learn how to add fractions with unlike denominators. The number choices in this activity allow students to find the sum of the partial products with reasoning and sense making. It is acceptable if students express a product as an expression with the sum of the partial products.
Lin and Han draw diagrams to find the value of .
Here is Jada’s way to multiply .
I know that 2 is , so is .
I also know that 3 is , so is .
Compare the different ways to find the value of .
How are they alike? How are they different?
The purpose of this activity is for students to continue to make sense of strategies for multiplying 2 mixed numbers. The previous activity introduced a variety of strategies for students to consider applying. In this activity, they have the option of choosing any 3 of the 4 problems to solve, and then reflect on the different strategies.
Choose any 3 expressions. Find the value of each product. Explain or show your reasoning.
“Today we multiplied mixed numbers by writing the numbers as fractions to find the product like Jada or with diagrams like Lin’s or like Han’s that shows the partial products.”
“What are some advantages or disadvantages of each way?” (The diagram helps to visualize the product because it shows how big the small parts are and how many there are. This works well mainly when the whole number is not too big and the fraction is not too complex, otherwise it’s hard to draw. The partial products diagram always works well to find the partial products, but I wasn’t always sure how to add some of them up. Sometimes, I wrote an addition expression for the product. Writing both factors as fractions is smooth and always works with no real disadvantages other than a bit of arithmetic that is unavoidable.)