Counting

Question 1

Inclusion-Exclusion Priciple

Answer 1

|A U B| = |A| + |B| - |A ∩ B|

Question 2

Multiplication Principle

Answer 2

If there are 2 or more independent choices to be made, then # of different possible outcomes of all choices is product of the # of possibilities of each choice

Question 3

Permutation

Answer 3

When the order does matter; nPk = n!/(n-k)!

Question 4

Combination

Answer 4

When the order does not matter; the number of ways k objects can be chosen from n objects is n choose k, or nCk = n!/(k!(n-k)!)

Question 5

Factorial notation

Answer 5

n! = n x (n-1) x (n-2) x … x 3 x 2 x 1 ; n unique objects can be arranged in n! ways.