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A prerequisite knowledge graph of 1590 learning concepts across 8subjects. Track what you've mastered and see exactly what you're ready to learn next — the topics whose prerequisites you've already met. Built on the Marble Open Skill Taxonomy.

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Finding a missing number in addition

Mathematics · Addition & Subtraction · conceptual

Understand subtraction as finding an unknown addend (e.g. 10 − 8 = ? is the same as 8 + ? = 10)

What mastery looks like

  • Solve 10 − 8 by thinking 'what do I add to 8 to make 10?'
  • Explain that subtraction can be thought of as a missing-addend problem
  • Use known addition facts to solve related subtraction problems

Check your understanding

Can Finding a missing number in addition see that '10 − 8 = ?' is the same as asking 'what do I add to 8 to reach 10?' — so they can use their adding knowledge to help with subtraction?