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Methods of Counting By Dr. Carol A. Marinas Fundamental Counting Principle Event M can occur in m...
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Transcript of Methods of Counting By Dr. Carol A. Marinas Fundamental Counting Principle Event M can occur in m...
Methods of Counting
By Dr. Carol A. Marinas
Fundamental Counting Principle
Event M can occur in m ways Event N can occur in n ways The event M followed by N is m*n ways
If Event M is flipping a coin, there are 2 outcomes.
If Event N is rolling a die, there are 6 outcomes.
So the number of outcomes of flipping a coin and rolling a die is 2 * 6 or 12 ways.
Can you list them?
Permutations of Unlike Objects
How many ways can you choose 2 marbles from the 5 different colored marbles above if order matters?
(G, R), (G,B), (G, W), (G, Y)
(R, G), (R, B), (R, W), (R, Y)
(B, G), (B,R), (B, W), (B, Y)
(W, G), (W, R), (W, B), (W, Y)
(Y, G), (Y, R), (Y, B), (Y, W)
Permutation Formula An arrangement of things in a
definite order with no repetition.nPr = n ! (n - r)!
5P2 = 5 ! (5 - 2)! = 5 * 4 ways
Combinations of Unlike Objects
How many ways can you choose 2 marbles from the 5 different colored marbles above if order does not matter?
(G, R), (G,B), (G, W), (G, Y)
(R, G), (R, B), (R, W), (R, Y)
(B, G), (B,R), (B, W), (B, Y)
(W, G), (W, R), (W, B), (W, Y)
(Y, G), (Y, R), (Y, B), (Y, W)
Combination Formula An arrangement of things in which
order does not matter with no repetition.
nCr = n !
r! (n - r)!
5C2 = 5 !
2! (5 - 2)! = (5 * 4)/2 ways or 10 ways
Permutation of Like Objects Before the objects were distinctly
different, what if some objects were alike?
How many ways can you arrange the letters in “tot”?
tot, tto, ott 3 ways
Permutation of Like Objects How many ways can you arrange the letters in
“Mississippi”? This would be a lot of work to list. There must be
an easier way! Formula n ! r1! r2! r3! … rk!For “tot”, it is 3 ! = 3 ways 2! 1!
Permutation of Like Objects
How many ways can you arrange the letters in “Mississippi”?
Formula n ! r1! r2! r3! … rk!For “Mississippi”, it is 11 ! = 34650
ways 1! 4! 4! 2!11 letters so n = 111 M, 4 I’s, 4 S’s, and 2 P’s
Thanks for Counting with me!