📐 Pre-Algebra

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20 Exam-Style Problems · Concepts · Explanations

📝 20 Problems
25 Min
📚 10 Units
25:00
0 / 20 answered

📖 Core Concepts & Key Formulas

Study these before taking the quiz · Memorize the highlighted formulas

1

Integers & Absolute Value

UNIT 1
|a| = distance from 0 on number line
−(−a) = a    |−a| = |a|
Adding integers: same sign → add & keep sign; different sign → subtract & take larger sign
Subtracting: a − b = a + (−b) (add the opposite)
Multiplying/Dividing: same signs → positive; different signs → negative
✏ Example
|−7| = 7  |  −3 − (−5) = −3 + 5 = 2  |  (−4)(−3) = 12
2

Fractions, Decimals & Percents

UNIT 2
a/b ÷ c/d = a/b × d/c
% = (part ÷ whole) × 100
LCM: find Least Common Multiple to add/subtract fractions
To divide fractions: multiply by the reciprocal (flip the second fraction)
Percent to decimal: divide by 100  |  Decimal to percent: multiply by 100
✏ Example
2/3 ÷ 4/5 = 2/3 × 5/4 = 10/12 = 5/6  |  35% = 0.35
3

Ratios, Proportions & Rates

UNIT 3
a/b = c/d → a × d = b × c (Cross-multiply)
Rate: ratio comparing two different units (e.g., miles per hour)
Unit rate: denominator = 1
Scale factor: ratio of similar figure measurements
✏ Example
3/x = 6/10 → 6x = 30 → x = 5
4

Algebraic Expressions

UNIT 4
Distributive: a(b + c) = ab + ac
Combine Like Terms: 3x + 5x = 8x
Term: a number, variable, or product of both
Coefficient: the number in front of a variable (in 4x, coefficient = 4)
Like terms must have the same variable AND same exponent
✏ Example
3(2x − 4) = 6x − 12  |  5x + 3x − 2 = 8x − 2
5

Linear Equations (One Variable)

UNIT 5
Goal: isolate the variable
Do same operation to both sides
Inverse operations: undo addition with subtraction, multiply with divide
Two-step: first undo addition/subtraction, then multiplication/division
Always check your answer by substituting back into the original equation
✏ Example
2x + 5 = 13 → 2x = 8 → x = 4 ✓ (check: 2×4+5=13)
6

Inequalities

UNIT 6
Multiply/Divide by NEGATIVE → FLIP the sign
−2x < 6 → x > −3
Symbols: < (less than), > (greater than), ≤ (≤), ≥ (≥)
Open circle: < or > (not included) | Closed circle: ≤ or ≥ (included)
Solution is a range of values, not just one number
✏ Example
3x − 4 ≥ 8 → 3x ≥ 12 → x ≥ 4 (closed circle at 4)
7

Coordinate Plane & Graphing

UNIT 7
Slope = (y₂ − y₁) / (x₂ − x₁) = rise/run
y = mx + b (slope-intercept form)
Origin (0,0) | Points (x, y) | x = horizontal, y = vertical
m = slope (steepness) | b = y-intercept (where line crosses y-axis)
Positive slope: goes up left to right | Negative: goes down
✏ Example
Slope from (1,2) to (3,8): (8−2)/(3−1) = 6/2 = 3
8

Exponents & Scientific Notation

UNIT 8
aᵐ × aⁿ = aᵐ⁺ⁿ   aᵐ ÷ aⁿ = aᵐ⁻ⁿ
(aᵐ)ⁿ = aᵐⁿ   a⁰ = 1   a⁻ⁿ = 1/aⁿ
Scientific notation: a × 10ⁿ where 1 ≤ a < 10
Large numbers: positive exponent | Small decimals: negative exponent
Square roots: √(a²) = a (for a ≥ 0)
✏ Example
x³ × x⁴ = x⁷  |  0.0035 = 3.5 × 10⁻³
9

Geometry: Area, Perimeter & Volume

UNIT 9
Rectangle: A = lw, P = 2(l+w)
Triangle: A = ½bh
Circle: A = πr², C = 2πr
Pythagorean: a² + b² = c²
Area = square units | Perimeter/Circumference = linear units
Rectangular prism volume: V = lwh | Cylinder: V = πr²h
Pythagorean theorem: only for RIGHT triangles; c = hypotenuse (longest side)
✏ Example
Right triangle: a=3, b=4 → c² = 9+16 = 25 → c = 5
10

Statistics: Mean, Median, Mode & Probability

UNIT 10
Mean = (sum of all values) / (number of values)
P(event) = favorable outcomes / total outcomes
Median: middle value when data is ordered (if even count, average the two middle)
Mode: value that appears most often (can be more than one or none)
Range = maximum − minimum | Probability: 0 ≤ P ≤ 1
✏ Example
Data: 2,4,4,6,8 → Mean=4.8, Median=4, Mode=4, Range=6

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