Meters and Kilometers

10 min

Narrative

This Number Talk encourages students to use what they know about multiples of 100, the relationship between hundreds and thousands, and properties of operations to mentally solve problems. The reasoning students do here will be helpful later in the lesson when students explore the relationship between kilometers and meters, and convert measurements from the former to the latter.

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
Teacher Instructions
  • Record answers and strategies.
  • Keep expressions and work displayed.
  • Repeat with each expression.

Student Task

Find the value of each expression mentally.

  • 3×1003 \times 100

  • 40×10040 \times 100

  • 43×10043 \times 100

  • 43×1,00043 \times 1,000

Sample Response

  • 300: 3 groups of 100 make 300.
  • 4,000: 10×10010 \times 100 is 1,000, so 40×10040 \times 100 is 4 times 1,000.
  • 4,300: It is the sum of 40×10040 \times 100 and 3×1003 \times 100, which is 4,000+3004,000 + 300.
  • 43,000: 1,000 is 10 times 100, so 43×1,00043 \times 1,000 is 10 times as much as 43×10043 \times 100.
Activity Synthesis (Teacher Notes)
  • “How does knowing 43×10043 \times 100 help you find 43×1,00043 \times 1,000?” (1,000 is 10 times 100, so if we know 43×10043 \times 100, we can multiply that by 10 to find 43×1,00043 \times 1,000.)
Standards
Building Toward
  • 4.NBT.5·Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.
  • 4.NBT.B.5·Multiply a whole number of up to four digits by a one-digit whole number, and multiply two two-digit numbers, using strategies based on place value and the properties of operations. Illustrate and explain the calculation by using equations, rectangular arrays, and/or area models.

20 min

15 min