Mathematical words!

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Across
  1. 1. "The total distance around a shape.",
  2. 3. "Combining two or more numbers.",
  3. 6. "A shape with five sides.",
  4. 11. "A shape with three sides.",
  5. 12. "A tool used to measure angles.",
  6. 14. "The difference between the highest and lowest numbers.",
  7. 15. "A shape with four equal sides and four right angles.",
  8. 16. "A shape with opposite sides equal and four right angles.",
  9. 17. "The amount of space a 3D object occupies.",
Down
  1. 1. "A tool used for writing or drawing.",
  2. 2. "Splitting into equal parts or groups.",
  3. 4. "A shape with seven sides.",
  4. 5. "Formed when two lines meet at a point.",
  5. 7. "Distance across a circle through its center.",
  6. 8. "A round shape with no corners.",
  7. 9. "Distance from the center to the edge of a circle.",
  8. 10. "The amount of space inside a shape.",
  9. 13. "Parts of a whole.",
  10. 14. "A tool used to measure length.",