More Multiplication

10 min

Narrative

The purpose of an Estimation Exploration is for students to practice the skill of estimating a reasonable answer based on experience and known information. It gives students a low-stakes opportunity to share a mathematical claim and the thinking behind it (MP3).

Launch

  • Groups of 2
  • Display the expression.
  • “What is an estimate that’s too high? Too low? About right?”
  • 1 minute: quiet think time
Teacher Instructions
  • “Discuss your thinking with your partner.”
  • 1 minute: partner discussion
  • Record responses.
  • Monitor for students who estimate by using 10,000×90010,000 \times 900.

Student Task

9,999 ×8969,999  \times 896

Record an estimate that is:

too low about right too high

Sample Response

Sample responses:

  • too low: 7,000,000–8,000,000
  • about right: 8,000,000–10,000,000
  • too high: 10,000,000–11,000,000

Synthesis

  • Invite students to share estimates.
  • “Why is 10,000×90010,000 \times 900 a good estimate for the product?” (10,000 is just 1 more than 9,999 and 896 is close to 900.)
  • “What is the value of 10,000×90010,000 \times 900? How do you know?” (9,000,000, because the two numbers have 6 factors of 10 combined.)
Standards
Addressing
  • 5.NBT.5·Fluently multiply multi-digit whole numbers using the standard algorithm.
  • 5.NBT.B.5·Fluently multiply multi-digit whole numbers using the standard algorithm.

20 min

15 min