How to Subtract By Adding

Investigate the claim that 999997=-3. Learners discover how to subtract large numbers using a quick method of addition. The video provides examples and shows how adding machines and computers apply this approach to subtraction.

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Instructional Ideas

  • Use board work to practice the subtraction by addition method
  • Have pupils race to complete a problem with the traditional algorithm versus the subtraction by addition method
Classroom Considerations

  • Expects a proficiency with the standard subtraction algorithm

  • Provides several examples
  • Connects the method to a real-life application

  • None