Introduction
One of the most important keys to success on the AP Statistics exam is knowing your formulas inside and out. While the College Board provides a formula sheet on test day, top students know that success comes from mastery and application—not just recognition.
This Ultimate AP Statistics Formula Sheet (2025 edition) covers everything you need:
- Probability rules
- Confidence intervals
- Hypothesis tests
- Regression equations
- Sampling distributions
- Chi-square, t-distribution, z-scores, and more
And unlike the official sheet, this guide includes explanations, when to use each formula, and common mistakes to avoid.
If you’re serious about scoring a 5, combine this resource with practice strategies from RevisionDojo, where students learn not just formulas—but how to apply them under exam pressure.
1. Core Probability Formulas
- Addition Rule: P(A ∪ B) = P(A) + P(B) – P(A ∩ B)
- Use for “A or B” events.
- Multiplication Rule (Independent Events): P(A ∩ B) = P(A) × P(B)
- Only valid if A and B are independent.
- Conditional Probability: P(A|B) = P(A ∩ B) / P(B)
- Read as “probability of A given B.”
- Complement Rule: P(Aᶜ) = 1 – P(A)
Common Mistake to Avoid: Forgetting to subtract overlap when events are not mutually exclusive.
2. Random Variables
- Expected Value (Mean): μx = Σ [x × P(x)]
- Variance: σ²x = Σ [(x – μx)² × P(x)]
- Standard Deviation: σx = √σ²x
Shortcut Variance Formula: σ²x = Σ [x²P(x)] – μ²
3. Normal Distribution Formulas
- z-Score: z = (x – μ) / σ
- Standardization: Converts any normal variable to standard normal (mean = 0, SD = 1).
- Empirical Rule:
- 68% within 1σ
- 95% within 2σ
- 99.7% within 3σ
Tip: Always draw a normal curve when solving problems—this avoids sign errors.
4. Sampling Distributions
- Standard Error (for proportions): SE = √[p(1 – p) / n]
- Standard Error (for means): SE = σ / √n
- Central Limit Theorem (CLT): For large n, the sampling distribution of x̄ is approximately normal.
Common Mistake to Avoid: Forgetting conditions for CLT (n ≥ 30, or population already normal).
5. Confidence Intervals
- Proportion: CI = p̂ ± z*√[p̂(1 – p̂)/n]
- Mean (σ known): CI = x̄ ± z*(σ/√n)
- Mean (σ unknown): CI = x̄ ± t*(s/√n)
- Difference of Proportions: CI = (p̂₁ – p̂₂) ± z*√[(p̂₁(1 – p̂₁)/n₁) + (p̂₂(1 – p̂₂)/n₂)]
- Difference of Means (σ unknown): CI = (x̄₁ – x̄₂) ± t*√[(s₁²/n₁) + (s₂²/n₂)]
Tip: Always include interpretation in context, e.g., “We are 95% confident that the true mean weight of apples lies between 140g and 150g.”
6. Hypothesis Testing
General Steps (always on FRQs):
- State hypotheses.
- H₀: parameter = value
- Hₐ: parameter >, <, or ≠ value
- Check conditions (random, normality, independence).
- Calculate test statistic.
- Find p-value.
- Conclusion in context.
Key Formulas:
- One-Proportion z-Test: z = (p̂ – p₀) / √[p₀(1 – p₀)/n]
- Two-Proportion z-Test: z = (p̂₁ – p̂₂) / √[p̂c(1 – p̂c)(1/n₁ + 1/n₂)]
- One-Sample t-Test (mean): t = (x̄ – μ₀) / (s/√n)
- Two-Sample t-Test (independent means): t = (x̄₁ – x̄₂) / √[(s₁²/n₁) + (s₂²/n₂)]
- Paired t-Test: t = (x̄d – μd) / (sd/√n)
7. Chi-Square Tests
- Test Statistic: χ² = Σ[(O – E)² / E]
- O = observed
- E = expected
Three Types:
- Goodness of Fit (1 variable vs expected distribution).
- Test of Homogeneity (compare distributions across groups).
- Test of Independence (association between 2 variables).
Degrees of Freedom:
- Goodness of Fit: df = categories – 1
- Independence/Homogeneity: df = (rows – 1)(columns – 1)
8. Regression & Correlation
- Equation of LSRL: ŷ = a + bx
- b = r(sy/sx)
- a = ȳ – b(x̄)
- Coefficient of Determination (R²): % of variation in y explained by x.
- Standard Error of Residuals (s): √[Σ(residual²) / (n – 2)]
Important: Always check scatterplot before regression—it must be roughly linear.
9. AP Statistics Exam Tips for Using Formulas
- Always write down the formula before plugging in numbers. (The AP rubric rewards method).
- Don’t just circle the number—interpret results in context.
- Check conditions (randomness, independence, normality) every time.
- Avoid “mechanical answers”—show understanding, not just calculations.
Conclusion
The AP Statistics exam doesn’t reward pure memorization—it rewards knowing when and how to apply formulas correctly. This Ultimate AP Statistics Formula Sheet (2025 edition) gives you all the essential tools, plus reminders on conditions, mistakes to avoid, and tips for full-credit answers.
For deeper practice with step-by-step applications, sample problems, and strategy breakdowns, use RevisionDojo’s AP Statistics prep resources—designed to help you apply every formula under exam conditions.
Frequently Asked Questions
Q: Do I need to memorize all these formulas for the AP Stats exam?
A: The College Board provides a formula sheet, but memorization helps you work faster and avoid confusion.
Q: How do I know which test (z, t, chi-square) to use?
A: Ask:
- Is it proportions (z) or means (t)?
- Is population σ known (z) or unknown (t)?
- Is it categorical data (chi-square)?
Q: What’s the most common formula mistake on the exam?
A: Forgetting to check conditions before using a test statistic or misapplying standard error formulas.
Q: Should I always write conditions on FRQs?
A: Yes—conditions are part of full-credit responses.
Q: Where can I practice applying these formulas?
A: At RevisionDojo, where you’ll find structured guides, practice sets, and problem walkthroughs built for AP Statistics students.
