📋 Formula sheet
All formulas with illustrations — print and hang on the wall!
📊 Statistics
Measures of centre
x̄ = Σxᵢ / n
Mean
σ = √(Σ(xᵢ-x̄)² / n)
Std deviation
z = (x - μ) / σ
Z-score
68-95-99.7 rule
μ ± 1σ → 68%
Within 1σ
μ ± 2σ → 95%
Within 2σ
μ ± 3σ → 99.7%
Within 3σ
Probability
P(A) = favourable / total
Probability
P(not A) = 1 - P(A)
Complement
0 ≤ P(A) ≤ 1
Always 0-1