Counting Flashcards
1
Q
what is combinatorics?
A
existence
enumeration: how many (cardinality)
extremality: “best”
2
Q
whats division rule
A
3
Q
how many 3 letter words from {a, u , c, g} that contain G
A
can do multiple ways.
1) 3 letter combos in order of where G first appears first, second, or third. so get 16+12+9.
2) add all (4^3) then subtract those without G (333)
4
Q
permutation v combination
A
permutation means order matters
5
Q
how calc permutation of r of n objects
A
n! / (n-r)!
6
Q
how calc r combination of n objects
A
n! / (r! * (n-r)!)
7
Q
A
