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 counting by ten and adding by place value. These understandings help students develop fluency and will be helpful later in this lesson when students develop ways to efficiently count large collections of objects. Students show an understanding of place value when they observe that the sums have the same digit in the ones place but the digit in the tens place changes (MP7).
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 sum mentally.
\(27 + 10\)
\(27 + 10 + 10\)
\(27 + 30\)
\(37 + 30\)
Student Response
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Activity Synthesis
“How did you use what you know about place value to find the sums?” (I knew I could start at 27 and count by ten. I knew 30 is the same as 3 tens. I know I could add the tens from each number together and the ones together.)


aligns: no