Attributes of Triangles and Quadrilaterals

10 min

Narrative

The purpose of this True or False is to elicit strategies students have for multiplying a one-digit number by a multiple of ten. This reasoning helps students deepen their understanding of the properties of operations and develop fluency.

When students use place value or properties of operations as strategies to divide, they look for and make use of structure (MP7).

Launch

  • Display one equation.
  • “Give me a signal when you know whether the equation is true and can explain how you know.”
  • 1 minute: quiet think time
Teacher Instructions
  • Share and record answers and strategy.
  • Repeat with each equation.

Student Task

Decide if each statement is true or false. Be prepared to explain your reasoning.

  • 3×60=9×103\times60=9\times10
  • 180=3×60180=3\times60
  • 6×40=24×106\times40=24\times10
  • 24×10=24024\times10=240

Sample Response

  • False: 9×10=909\times10=90. 2×602\times60 is 120, which is more than 90, so this is false.
  • True: I could think of 3×603\times60 as 18×1018\times10, which is 180.
  • True: If I decompose 40 into 4×104\times10, then I can multiply the 6×46\times4 to get 24. I still have to multiply by the 10 so it’s 24×1024\times10.
  • True: I know that 10×1010\times10 is 100. If I double 10, then I have 20×10=20020\times10=200. Four more tens is 40. 200+40=240200+40=240
Activity Synthesis (Teacher Notes)
  • “How can you explain your answer without finding the value of both sides?”
  • Consider asking:
    • “Who can restate _____’s reasoning in a different way?”
    • “Does anyone want to add on to _____’s reasoning?”
Standards
Addressing
  • 3.NBT.3·Multiply one-digit whole numbers by multiples of 10 in the range 10—90 (e.g., 9 × 80, 5 × 60) using strategies based on place value and properties of operations.
  • 3.NBT.A.3·Multiply one-digit whole numbers by multiples of 10 in the range 10–90 (e.g., <span class="math">\(9 \times 80\)</span>, <span class="math">\(5 \times 60\)</span>) using strategies based on place value and properties of operations.

15 min

20 min