standard_description: Apply and extend previous understandings of division to divide unit fractions by whole numbers and whole numbers by unit fractions. (Students able to multiply fractions in general can develop strategies to divide fractions in general, by reasoning about the relationship between multiplication and division. But division of a fraction by a fraction is not a requirement at this grade.)
problem_activity: Narrative
The purpose of this Number Talk is for students to demonstrate strategies and understandings they have for multiplying multi-digit whole numbers. These understandings help students develop fluency. The products in the number talk get increasingly more cumbersome to keep track of mentally so students can identify times when products are more easily found mentally and when the algorithm, with pencil and paper, might be preferable.
Launch
Display one problem.
“Give me a signal when you have an answer and can explain how you got it.”
Activity
1 minute: quiet think time
Record answers and strategy.
Keep problems and work displayed.
Repeat with each problem.
Student Facing
Find the value of each expression mentally.
\(230 \times 10\)
\(230 \times 12\)
\(230 \times 15\)
\(232 \times 15\)
Student Response
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Activity Synthesis
“Which problem was the most challenging to solve mentally? Why do you think so?” (Answers vary, but students will likely mention one of the last three because there are different products to keep track of and add.)


aligns: no