The ACT Math test is a 60-minute, 60-question assessment designed to measure the mathematical skills students have typically acquired in courses taken up to the beginning of grade 12. This cheat sheet provides essential concepts, formulas, and strategies to help you succeed.
Structure of the ACT Math Section
60 questions in 60 minutes (1 minute per question average)
Questions increase in difficulty from 1-60
Five topic areas with approximate percentages of questions:
Pre-Algebra (20-25%) Questions 1-15
Elementary Algebra (15-20%) Questions 6-20
Intermediate Algebra (15-20%) Questions 16-40
Coordinate Geometry (15-20%) Questions 21-50
Plane Geometry (20-25%) Questions 26-55
Trigonometry (5-10%) Questions 46-60
Calculator permitted for all questions
No formula sheet provided
Tip: The first 30 questions should be completed easily and quickly to save time for harder problems later. Don't spend more than 1-2 minutes on any question initially.
Pre-Algebra Concepts
Operations with Fractions
Adding/subtracting: Find a common denominator
Multiplying: Multiply numerators and denominators separately
Dividing: Multiply by the reciprocal of the second fraction
Simplify fractions by dividing numerator and denominator by their GCF
Operations with Decimals
Adding/subtracting: Line up decimal points
Multiplying: Multiply as integers, then place decimal point (sum of decimal places)
Dividing: Move decimal in divisor to make it whole, move decimal in dividend same amount, then divide
Percentages
Percentage = (Part Whole) 100%
Part = Whole Percentage (as a decimal)
Whole = Part Percentage (as a decimal)
Proportions
a/b = c/d
Cross-multiply: ad = bc
Basic Statistics
Mean: Sum of values number of values
Median: Middle value when arranged in order
Mode: Most frequently occurring value
Range: Difference between highest and lowest values
Basic Probability
P(Event) = Favorable outcomes Total possible outcomes
P(A and B) = P(A) P(B) (for independent events)
P(A or B) = P(A) + P(B) - P(A and B)
Elementary Algebra Concepts
Variables and Expressions
Combine like terms
Apply distributive property: a(b + c) = ab + ac
Evaluate expressions by substituting values
Solving Linear Equations
Isolate the variable using inverse operations
Remember to do the same operation to both sides
Check your solution by substituting back
Inequalities
Warning: When multiplying or dividing an inequality by a negative number, reverse the inequality sign.
Systems of Equations
Substitution: Solve one equation for a variable and substitute into the other
Elimination: Add or subtract equations to eliminate one variable
Exponents
a^m a^n = a^(m+n)
(a^m)^n = a^(mn)
(ab)^n = a^n b^n
a^m a^n = a^(m-n)
a^0 = 1 (if a 0)
a^(-n) = 1/a^n
Radicals
(ab) = a b
(ab) = a b
a = |a|
Intermediate Algebra Concepts
Quadratic Equations
ax + bx + c = 0
Quadratic formula: x = (-b (b-4ac)) / 2a
Factoring: Find two numbers that multiply to ac and add to b
Vertex form: y = a(x-h) + k, where vertex is (h,k)
Functions
Domain: Set of all possible input values (x)
Range: Set of all possible output values (y)
f(x) notation: f(g) means evaluate the function at x = g
Composition: f(g(x)) means apply function g to x, then apply function f to the result
Polynomials
Adding/subtracting: Combine like terms
Multiplying: Use distributive property (FOIL for binomials)
Dividing: Long division or synthetic division
Complex Numbers
i = (-1), so i = -1
a + bi form for complex numbers
(a+bi)(c+di) = ac - bd + (ad+bc)i
Sequences and Series
Arithmetic sequence: Each term is previous term plus constant difference d
a_n = a_1 + (n-1)d
Geometric sequence: Each term is previous term multiplied by constant ratio r
a_n = a_1 r^(n-1)
Coordinate Geometry Concepts
Distance and Midpoint Formulas
Distance between (x, y) and (x, y): [(x-x) + (y-y)]
Midpoint between (x, y) and (x, y): ((x+x)/2, (y+y)/2)
Slope
Slope (m) = (y-y) / (x-x)
Slope-intercept form: y = mx + b
Point-slope form: y-y = m(x-x)
Parallel and Perpendicular Lines
Parallel lines have equal slopes: m = m
Perpendicular lines have slopes that are negative reciprocals: m m = -1
Absolute value equations (y = |ax + b|): V-shaped graphs
Plane Geometry Concepts
Angles
Complementary angles sum to 90
Supplementary angles sum to 180
Vertical angles are equal
Angles around a point sum to 360
Interior angles of a triangle sum to 180
Triangles
Area = (1/2) base height
Pythagorean theorem: a + b = c (for right triangles)
Special Right Triangles
30-60-90 triangle: sides are 1, 3, 2 (short leg opposite 30)
45-45-90 triangle: sides are 1, 1, 2
Triangle Classification
Equilateral: all sides equal, all angles 60
Isosceles: at least two sides equal, base angles equal
Scalene: all sides different
Right: one 90 angle
Quadrilaterals
Shape
Properties
Area Formula
Rectangle
Opposite sides equal, all angles 90
length width
Square
All sides equal, all angles 90
side
Parallelogram
Opposite sides parallel and equal
base height
Trapezoid
One pair of parallel sides
(1/2) (sum of parallel sides) height
Circles
Area = r
Arc length = (/360) 2r
Tangent line is perpendicular to radius at point of tangency
Polygons
Sum of interior angles = (n-2) 180 (where n is the number of sides)
Trigonometry Concepts
Basic Trig Functions
sin() = opposite/hypotenuse
cos() = adjacent/hypotenuse
tan() = opposite/adjacent = sin()/cos()
Reciprocal Trig Functions
csc() = 1/sin()
sec() = 1/cos()
cot() = 1/tan() = cos()/sin()
Unit Circle Values
Angle
0
30
45
60
90
sin
0
1/2
2/2
3/2
1
cos
1
3/2
2/2
1/2
0
tan
0
3/3
1
3
Undefined
Trig Identities
sin() + cos() = 1
tan() + 1 = sec()
1 + cot() = csc()
sin(2) = 2sin()cos()
cos(2) = cos() - sin() = 1 - 2sin() = 2cos() - 1
Test-Taking Strategies
Time Management
Spend roughly 1 minute per question
Don't get stuck on difficult problems; mark them and return if time permits
Set mini-time goals: Question 20 by 20 minutes, Question 40 by 40 minutes
Answer easier questions first to build confidence
Process of Elimination
Eliminate obviously wrong answers to improve your odds
Use estimation to narrow down choices
Test answer choices when appropriate (especially for algebra problems)
Problem-Solving Techniques
Draw diagrams for geometry problems
Substitute numbers for variables in algebra problems
Look for patterns and relationships
Work backwards from the answer when stuck
Break complex problems into smaller, manageable parts
Tip: There's no penalty for wrong answers on the ACT, so never leave a question blank. Even if you can only eliminate one answer choice, you should guess from the remaining options.
Essential Formulas to Memorize
Geometric Formulas
Rectangle: Perimeter = 2(l+w); Area = lw
Square: Perimeter = 4s; Area = s
Triangle: Perimeter = a+b+c; Area = (1/2)bh
Circle: Circumference = 2r; Area = r
Cylinder (surface area): A = 2r + 2rh
Sphere (surface area): A = 4r
Rectangular Prism (volume): V = lwh
Cylinder (volume): V = rh
Sphere (volume): V = (4/3)r
Algebraic Formulas
Slope: m = (y-y)/(x-x)
Midpoint: ((x+x)/2, (y+y)/2)
Discriminant: = b - 4ac (determines number of solutions)
Trigonometric Formulas
Law of Sines: a/sin(A) = b/sin(B) = c/sin(C)
Tip: Practice using these formulas in context. Being able to recognize when to apply a formula is as important as knowing the formula itself.
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