WGU C 955: Probability Statistics Study Guide: Complete Exam Prep 2027 update with complete solutions

SECTION 1 Fractions, Decimals, and Percentages These are three different ways to represent the same number. Mastering conversion between them is essential for everything else in this course. Converting Between Forms Conversion Method Fraction → Decimal Example Divide top by bottom Decimal → Percentage 3/4 = 3 ÷ 4 = 0.75 Multiply by 100 Percentage → Decimal 0.75 × 100 = 75% Divide by 100 Fraction → Percentage 75% ÷ 100 = 0.75 Divide then multiply by 100 3/4 = 0.75 → 75% Key Operations Finding a percentage OF a number: What is 30% of 200? → 0.30 × 200 = 60 Finding what percentage one number is of another: 15 is what percent of 60? → 15 ÷ 60 = 0.25 = 25% Percentage increase/decrease: Example: Price goes from $80 to $100 (New − Old) ÷ Old × 100 (100 − 80) ÷ 80 × 100 = 20 ÷ 80 × 100 = 25% increase Memory Tip: To go from % to decimal: move decimal LEFT 2 places (45% → 0.45) To go from decimal to %: move decimal RIGHT 2 places (0.33 → 33%) SECTION 2 Basic Algebra Solving for an unknown variable by doing the same operation to both sides of the equation. Solving Equations The golden rule: whatever you do to one side, do to the other. Solving Inequalities Same as equations with one critical exception: if you multiply or divide by a negative number, flip the inequality sign. Symbol Meaning Greater than Less than  Greater than or equal to  Less than or equal to Order of Operations — PEMDAS Letter Operation Do This First? P Parentheses Yes — always first E Exponents Second M/D Multiplication / Division Third (left to right) Example 1: Solve 3x + 5 = 20 Step 1: Subtract 5 from both sides → 3x = 15 Step 2: Divide both sides by 3 → x = 5 Example 2: Solve 2x − 8 = 12 Step 1: Add 8 to both sides → 2x = 20 Step 2: Divide both sides by 2 → x = 10 Example: Solve −2x 8 Divide both sides by −2 → FLIP the sign → x −4 Letter A/S Operation Addition / Subtraction Do This First? Last (left to right) Example: 3(2 + 4)² − 5 Step 1: Parentheses: (2+4) = 6 Step 2: Exponent: 6² = 36 Step 3: Multiply: 3 × 36 = 108 Step 4: Subtract: 108 − 5 = 103 SECTION 3 Descriptive Statistics — Single Variable Descriptive statistics summarize and describe the key features of a dataset. Know every measure cold — these will appear throughout the exam. The 5 Core Measures Add all values together, then divide by how many there are. The mean is affected by extreme values (outliers). For an odd count: take the middle value. For an even count: average the two middle values. NOT affected by outliers. A dataset can have no mode, one mode, or multiple modes.