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  1. 1Adding 2/3 + 3/4
  2. 2Subtracting fractions
  3. 3Multiplying fractions
  4. 4Dividing fractions
  5. 5Fraction of a number
  6. 6Multiplying decimals
  7. 7Dividing by a decimal
  8. 8Finding 15% of 240
  9. 9Percent increase
  10. 10Finding a sale price
  11. 12Sharing $120 in a ratio
  12. 13Unit rate, proportions
  13. 14Speed from distance and time
  14. 15Price per ounce, unit rate
  15. 16Order of operations
  16. 17Order of operations
  17. 18Order of operations, integers
  18. 19Adding and subtracting integers
  19. 20Solving x/4=9
  20. 21Solving 3x−7=20
  21. 24Area and perimeter of rectangle
  22. 25Area of a triangle
  23. 26Area of a circle
  24. 27Circumference of a circle
  25. 30Angle sum of a triangle
  26. 31Angles on a straight line
  27. 32Base angles of isosceles triangle
  28. 33Mean of a data set
  29. 34Median and mode
  30. 36Probability of one outcome

31Angles on a straight line

Two angles on a straight line measure 3x and 2x + 30 degrees. Find x.

Since the two angles lie on a straight line, they add to 180°, giving x = 30. From 3x + (2x + 30) = 180, we get 5x = 150, so x = 30. Check: 90° + 90° = 180°.

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