Suppose there are n₁ ways for E₁ to occur, and n₂ ways for event E₂ to occur we cannot do both E₁ and E₂.
Addition Principle
Suppose there are n₁ ways for E₁ to occur, and each possible way that E₁ occurs allows exactly n₂ ways for event E₂ to occur.
Multiplication Principle
The number of different ways we can arrange a number of items.
Permutations
Permutations of n object taking r at a time
nPr = n!/(n-r)!
Permutations of Identical objects
P= n!/r₁!r₂!r₃!*r₄!…
Circular Permutations
P(n)=(n-1)!
Arrangement of objects where the order in which the objects are selected does not matter.
Combination
“Selection”
Combination
“Arrangement”
Permutations
Combination
nCr = n!/(n-r)!r!