ADV002 · Advanced mathematics · Classes 11–12
Combinatorics
Counting arrangements (order matters) and selections (order doesn’t).
Combinatorics📐 Formula
ⁿPᵣ = n! ÷ (n − r)!; ⁿCᵣ = n! ÷ [r!(n − r)!]
✏️ Worked example
n = 5, r = 3: ⁵P₃ = 60, ⁵C₃ = 10.
🌍 Where it is used
Passwords, team selection and lotteries.
❓ Quick check
⁴C₂ =