standard_description: Apply properties of operations as strategies to multiply and divide. (Students need not use formal terms for these properties.) ^( )Examples: If 6 × 4 = 24 is known, then 4 × 6 = 24 is also known. (Commutative property of multiplication.) 3 × 5 × 2 can be found by 3 × 5 = 15, then 15 × 2 = 30, or by 5 × 2 = 10, then 3 × 10 = 30. (Associative property of multiplication.) Knowing that 8 × 5 = 40 and 8 × 2 = 16, one can find 8 × 7 as 8 × (5 + 2) = (8 × 5) + (8 × 2) = 40 + 16 = 56. (Distributive property.)
problem_activity: Narrative
The purpose of this Number Talk is to elicit strategies and understandings students have for multiplication by 10. These understandings help students develop fluency and will be helpful later in this lesson when students need to be able to represent and solve a problem involving groups of 10.
When students reason why as one factor increases by 1, the product increases by 10, they look for and express the regularity they notice in the expressions (MP8).
Launch
Display one expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Activity
Record answers and strategy.
Keep expressions and work displayed.
Repeat with each expression
Student Facing
Find the value of each expression mentally.
\(1\times10\)
\(2\times10\)
\(3\times10\)
\(4\times10\)
Student Response
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Activity Synthesis
“What pattern do we see as we look at all of the problems? Why is that happening?” (The factor that isn’t 10 goes up by 1 each time. The products increase by 10 because I have one more group of 10.)
Consider asking:
“Did anyone use a different strategy”?
“Did anyone have the same strategy but would explain it differently?”


aligns: no