standard_description: Interpret multiplication as scaling (resizing), by:
- Explaining why multiplying a given number by a fraction greater than 1 results in a product greater than the given number (recognizing multiplication by whole numbers greater than 1 as a familiar case); explaining why multiplying a given number by a fraction less than 1 results in a product smaller than the given number; and relating the principle of fraction equivalence a/b = (n×a)/(n×b) to the effect of multiplying a/b by 1.
- Comparing the size of a product to the size of one factor on the basis of the size of the other factor, without performing the indicated multiplication.
problem_activity: Narrative
The goal of this activity is for students to examine different ways to write the product of a three-digit number and a two-digit number as a sum of partial products. Students match sets of partial products which can be put together to make the full product. Students are provided blank diagrams, familiar from the previous lesson, that they may choose to use to support their reasoning. In the activity synthesis, students relate the expressions and diagrams to equations to prepare them to analyze symbolic notation for partial products in the next activity.
When students relate partial products and diagrams to the product
\(245 \times 35\)
they look for and identify structure (MP7).
MLR8 Discussion Supports.
Display the following sentence frame to support small-group discussion: “I noticed _____ , so I matched . . . .” Encourage students to challenge each other when they disagree.
Advances: Speaking, Conversing
Required Materials
Materials to Copy
Partial Product Expressions
Required Preparation
Create a set of cards from the blackline master for each group of 2.
Launch
Groups of 2
Display first image from student book.
“What product does this rectangle represent?” (
\(245 \times 35\)
)
“Today, you are going to take turns with your partner picking expressions that can be added together to give the product
\(245 \times 35\)
. You can use the diagrams to explain your reasoning, if they are helpful.”
Activity
10 minutes: partner work time
Monitor for students who:
use the diagram to determine which expressions they will use.
look at the expressions and think about how they could be used to find the full product.
compute the full product in different ways.
Student Facing
[IMG]
[IMG]
[IMG]
Take turns picking out a set of expressions that are equal to
\(245 \times 35\)
when added together. Use the diagrams if they are helpful.
Explain how you know the sum of your expressions is equal to
\(245 \times 35\)
.
What is the value of
\(245 \times 35\)
? Explain or show your reasoning.
Student Response
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Advancing Student Thinking
If students do not choose correct expressions to represent a sum that is equal to
\(245 \times 35\)
, refer to one of the empty boxes in the diagram and ask, “Which multiplication expression represents this partial product?”
Activity Synthesis
Invite previously selected students to share their strategies. As students share, record their reasoning with equations.
Display:
\(245 \times 30 + 245 \times 5  = 245 \times 35\)
“How do you know this equation is true?” (I can put the 30 and 5 together since they are both multiplied by 245. I see that
\(245 \times 30\)
is the top part of the diagram and
\(245 \times 5\)
is the bottom part. Together that’s the whole diagram.)


aligns: no