Counting & Probability

Question 1

Permutations (order matters)

Answer 1

ₙPₖ=n!/((n-k)!)

n=total number of objects from which you are choosing k objects

Question 2

Combinations (order doesn’t matter)

Answer 2

ₙCₖ=n!/(k!(n-k)!)

n=total number of objects from which you are choosing k objects

Question 3

Fundamental Theorem of Counting

Answer 3

If one event has n possible outcomes and another event has m possible outcomes, the total number of events if both events occur is m × n.

Question 4

complementary counting

Answer 4

total - what we don’t want = what we want

Often uses the words “at least”