Give me 20 words and clues math related

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Across
  1. 3. Unknown quantity
  2. 7. Study of shapes
  3. 12. Equal ratios
  4. 15. Subject
  5. 16. Number with a point
  6. 17. Average of a set of numbers
  7. 18. Fixed value
  8. 19. Out of one hundred
Down
  1. 1. Square root symbol
  2. 2. Part of a whole
  3. 4. Input and Output relationship
  4. 5. Visual representation of data
  5. 6. Rise over run
  6. 8. Power of a number
  7. 9. Statement of equality
  8. 10. Difference between highest and lowest values
  9. 11. Most frequent value
  10. 13. Comparison of two quantities
  11. 14. Middle value in a sorted set
  12. 18. Study of change
  13. 20. Solving for variables