26 Need to Know Math Concepts for the ACT

The ACT math section isn't so much hard as it is tricky. Unlike school where you spend a few weeks working on a unit and then take a test on it, the ACT math test covers material that goes back as far as middle school for some students. One of the first steps in getting a great math score is mastering these 26 key concepts.

  1. Sum: Addition

  2. Difference: Subtraction

  3. Product: Multiplication

  4. Quotient: Division

  5. Order of Operations / PEMDAS: Parentheses, Exponents, Multiplication/Division, Addition/Subtraction

  6. Mean, Median, Mode

  7. Mean means average: Add up all the numbers and divide by how many items there are.

  8. Median: Put the numbers in order from smallest to largest. Then find the number in the exact middle. If the number is even, find the average of the 2 number in the middle.

  9. Mode: The number that appears most often.

  10. Powers, Exponents, and Roots

  11. When you multiply common bases with exponents, add the exponents

  12. Ex. x² * x⁵ = x⁷

  13. When you divide common bases with exponents, subtract the exponents

  14. Ex. x⁷ / x² = x⁵

  15. When you raise a base with an exponent to another exponent, multiply the exponents

  16. (x²)⁴ = x⁸

  17. Any number raised to 0 equals 1

  18. Ex. 10170 = 1

  19. Absolute Value: The distance from zero on the number line. It is the positive version of a number.

  20. │-2 │= 2 and │2│ = 2

  21. Arithmetic sequence: There is a common difference or addition

  22. 2, 5, 8, 11, 14 or 15, 10, 5, 0, -5

  23. Geometric sequence: There is a common multiple

  24. 3, 9, 27, 81 or 45, 15, 3, 1, 1/3

  25. Bisect: To cut an angle or line in half

  26. Chord: Any line segment that both ends on a circle

  27. A diameter is the longest chord of any circle

  28. Complement: Two angles that add up to 90°

  29. Supplement: Two angles that add up to 180°

  30. Consecutive: Numbers that follow each other directly.

  31. Ex. 5, 6, 7

  32. Consecutive odd numbers: 5, 7, 9, 11

  33. Integer: Any number that doesn’t have a decimal or a fraction.

  34. Ex. -1 or 17

  35. Real number: Any number that is not imaginary

  36. Ex. -17 , pi , 3.666666667

  37. Imaginary numbers: The square root of a negative number

  38. Ex. √(-16) = 4i or √(-25) = 5i

  39. Remember: i² = -1

  40. Prime Numbers: Can only be divided by 1 and themselves

  41. Ex. 2, 3, 5, 7, 11, 13

  42. 1 is not a prime number

  43. 2 is the only even prime number

  44. Rational number: Any number that ends or repeats.

  45. Ex. 7, -4.83, 3/4, 0.1616161616161616...

  46. Irrational: A number that doesn’t end or repeat.

  47. Ex. pi, √(7), 1/3

  48. Greatest Common Factor: The largest number a group of numbers can be divided by.

  49. Ex. The greatest common factor of 50 & 75 is 25

  50. Least Common Multiple: The smallest number that a group of numbers can multiply into.

  51. Ex. The least common multiple of 4 & 7 is 28

  52. Percent increase/decrease: Find the difference between the two numbers. Then divide the difference by the original.

  53. Ex. Find the percent increase from 3 to 5: Difference is 2, original is 3. The percent increase is 2/3 or 66%.

  54. Probability: The chance you get the result you want. Divide the number of times you get what you want by the total times that is possible.

  55. Ex. If there are 5 red balls in a bag of 20 balls, what is the probability you randomly pull out a red ball?

  56. Want is 5, total is 20, 5/20 is 1/4 or 25%

  57. Sandwich problems AKA The Fundamental Counting Principle: Multiply the amount of items in each category by each other.

  58. Ex. If they ask how many possible combinations of sandwiches can be made with 4 types of bread, 3 types of cheese, and 5 types of meat: Multiply 4 X 3 X 5 = 60

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