Basic math symbols

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Across
  1. 5. ÷
  2. 7. ≠
  3. 9. a²
  4. 11. <
  5. 14. * it is also used for multiplication
  6. 15. []
  7. 17. ()
  8. 18. ≤
  9. 19. mod
  10. 20. >
Down
  1. 1. ≥
  2. 2. ppm
  3. 3. 3√a
  4. 4. +
  5. 6. %
  6. 8. ppt
  7. 10. .
  8. 12. / it is also used for division
  9. 13. -
  10. 16. ‰