This Number Talk helps students develop strategies to find multiples of 12 mentally, using place value and the distributive property. This work prepares students for converting measurements in feet to measurements in inches.
Launch
Display the first expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Teacher Instructions
Record students’ answers and strategies.
Keep the expressions and the work displayed.
Repeat with each expression.
Student Task
Find the value of each expression mentally.
45×2
45×10
45×12
46×12
Sample Response
90: I doubled 40 and added 10.
450: Every digit shifts one place to the left because I multiplied by 10.
540: I added the previous two products.
552: I just added another 12.
Activity Synthesis (Teacher Notes)
“How are the values of the products 45×12 and 46×12 related?” (There is one more 12 in 46×12.)
Standards
Building Toward
5.MD.1·Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.
5.MD.A.1·Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.
15 min
20 min
Knowledge Components
All skills for this lesson
No KCs tagged for this lesson
Multi-step Conversion Problems: Customary Lengths
10 min
Narrative
This Number Talk helps students develop strategies to find multiples of 12 mentally, using place value and the distributive property. This work prepares students for converting measurements in feet to measurements in inches.
Launch
Display the first expression.
“Give me a signal when you have an answer and can explain how you got it.”
1 minute: quiet think time
Teacher Instructions
Record students’ answers and strategies.
Keep the expressions and the work displayed.
Repeat with each expression.
Student Task
Find the value of each expression mentally.
45×2
45×10
45×12
46×12
Sample Response
90: I doubled 40 and added 10.
450: Every digit shifts one place to the left because I multiplied by 10.
540: I added the previous two products.
552: I just added another 12.
Activity Synthesis (Teacher Notes)
“How are the values of the products 45×12 and 46×12 related?” (There is one more 12 in 46×12.)
Standards
Building Toward
5.MD.1·Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.
5.MD.A.1·Convert among different-sized standard measurement units within a given measurement system (e.g., convert 5 cm to 0.05 m), and use these conversions in solving multi-step, real world problems.