PERMUTATION
nPr = n! / (n−r)!
ORDER matters → use P
"Placing people in seats"
COMBINATION
nCr = n! / r!(n−r)!
ORDER doesn’t matter → use C
"Choosing a team"
PROBABILITY
P(A) = favorable / total
Always 0 to 1
"Part out of whole"
ORDER CHECK
P or C?
Ask: “Does swapping change it?”
YES → P · NO → C