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Permutations Permutations and and
CombinationsCombinations
Standards:MM1D1b. Calculate and use simple permutations and combinations.
How many different lunches could you order if there were 4 different sandwiches, 3 different side orders and 4 different drinks?
How many different ice cream sundaes could you order if there were 3 different flavors of ice cream, 4 different sauces, and 2 different toppings?
Ice Cream Sundae
Chocolate
Strawberry
Pineapple
Caramel
Lunch
Suppose you wanted lunch and an ice cream sundae. What would you do?
Suppose you wanted either lunch or an ice cream sundae. What would you do?
Ice Cream Sundae
Chocolate
Strawberry
Pineapple
Caramel
Lunch
When using the counting principle,
the word “and” means to multiply.
x
When using the counting principle,
the word “or” means to add.
+
N factorial
For any positive integer n, the product of integers from 1 to n is called n factorial and is written as n!. The value of 0! Is defined to be 1.
Examples:1. 5!5 · 4 · 3 · 2 · 1 = 2. 9!9 · 8 · 7 · 6 · 5 · 4 · 3 · 2 · 1 =
Permutations
A permutation is an arrangement of objects in which order is important. The number of permutations of n objects is given by nPn = n!. The number of permutations of n objects taken r at a time, where r ≤ n, is given by nPr = n!
(n – r)!
Combinations
A combination is a selection of objects in which order is NOT important. The number of combinations of n objects taken r at a time, where r ≤ n, is given by
nCr = n!
(n – r)! · r!