Standard Algorithm to Add and Subtract

10 min

Narrative

The purpose of an Estimation Exploration is to practice the skill of estimating a reasonable answer based on experience and known information.

The expression allows students to preview the work of this lesson and give teachers insight into how students think about subtraction.

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.

Student Task

Estimate the difference: 42,050−3,79042,050 - 3,790.

Record an estimate that is:

too low about right too high

Sample Response

Sample response:
  • Too low: 35,000
  • Too high: 40,000
  • About right: 38,000
Activity Synthesis (Teacher Notes)
  • “Is anyone’s estimate less than 30,000?”
  • “Is anyone’s estimate greater than 40,000?”
  • “Based on this discussion, does anyone want to revise their estimate?”
  • “Let’s find out how to add and subtract numbers like these.”
Standards
Building Toward
  • 4.NBT.4·Fluently add and subtract multi-digit whole numbers using the standard algorithm.
  • 4.NBT.B.4·Fluently add and subtract multi-digit whole numbers using the standard algorithm.

15 min

20 min