Figure it out

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Across
  1. 5. a letter that represents an unknown number
  2. 6. Border
  3. 7. 3.14159...
  4. 10. Math with letters
  5. 11. subtract the smallest number from the largest value
  6. 14. planes Four quadrants
  7. 16. Numbers with Points
  8. 18. Value Numerical numbers
  9. 19. Counting numbers and their opposites
Down
  1. 1. Mass
  2. 2. Supporter/power
  3. 3. circular/boundary
  4. 4. The centered number in an ordered list
  5. 8. Part, Share, Division
  6. 9. Proportion
  7. 12. Diagrams/Charts
  8. 13. A number out of 100
  9. 15. The most frequent value in a group of numbers
  10. 17. The average set of numbers
  11. 18. Two dimensional measure