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15.3 – Permutations and Combinations. Objective: You should be able to solve problems involving permutations and combinations. Permutation. Order of selection IS important . Ex. Selecting President, Vice President, and Treasurer ***There are 6 permutations of the letters A, B, and C :
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15.3 – Permutations and Combinations Objective: You should be able to solve problems involving permutations and combinations.
Permutation • Order of selection IS important. • Ex. Selecting President, Vice President, and Treasurer • ***There are 6 permutations of the letters A, B, and C: ABC, ACB, BCA, BAC, CAB, and CBA. • Since there are 3 choices for the 1st letter, 2 choices for the 2nd, and 1 choice for the 3rd, there are 3∙2∙1 = 3! = 6 ways to arrange the letters. • In general, the number of permutations of nobjects is n!
Example: • You have homework assignments from 5 different classes to complete this weekend. In how many different ways can you complete the assignments?
Permutations of n objects taken r at a time • The number of permutations of r objects taken from a group of n distinct objects is denoted by nPr= Ex. 10P4= =5040
Example: • The Bulls have two starting positions open, a point guard and a small forward. If 15 people who are qualified for either position try out, in how many ways can the opening be filled?
Combination • a selection of r objects from a group on n objects where the order is NOT important. • Ex. Selecting a governing council of 3 people • nCr= Ex. 10C4= = 210
Example: • The Celtics have two non-starting forward positions available. In how many ways can the positions be filled if 22 people try out?
Example: • For a certain raffle, 845 tickets are sold. • a. In how many ways can four $50 gifts cards be awarded? • b. In how many ways can a $100, a $50, a $20, and a $10 gift card be awarded?
Example: • At the Denny’s, an omelet can be ordered plain or with any or all of the following fillings: cheese, onions, peppers. How many different kinds of omelets are possible?
Example: • a) You are taking a vacation and can visit as many as 5 different cities and 7 different attractions. Suppose you want to visit exactly 3 different cities and 4 different attractions. How many different trips are possible?
Example cont. • b) Suppose you want to visit at least 8 locations (cities or attractions). How many different types of trips are possible?