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Education Concept Tracker

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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Mental addition and subtraction (age 7+)

Mathematics · Addition & Subtraction · procedural

Mentally add and subtract a three-digit number and ones

What mastery looks like

  • Calculate 345 + 7 mentally
  • Calculate 462 − 5 mentally
  • Explain that only the ones digit changes (unless bridging through a ten)

Check your understanding

Can Mental addition and subtraction (age 7+) work out '436 + 7' or '521 − 8' in their head — keeping the hundreds and tens unchanged while adjusting just the ones?