Math crossword puzzle

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Across
  1. 4. An answer to multiplication
  2. 6. amount of increase from the cost to selling
  3. 7. the average of a few numbers
  4. 10. The amount of money deposited in an account
  5. 12. letter in question
  6. 14. an angle under 180 and over 90 degrees
  7. 15. measuring the border of a shape
  8. 17. the inside of a closed shape
  9. 18. a number without a variable
  10. 19. an answer to subtract
Down
  1. 1. an answer to division
  2. 2. measuring steepness
  3. 3. an answer to addition
  4. 5. A constant for multiplying a variable
  5. 8. A very important subject
  6. 9. the between number in order
  7. 11. an angle under 90 degrees
  8. 13. a negative or positive number
  9. 16. the difference between the highest and lowest
  10. 20. angle a 90 degree angle