JMB Chapter 2 c Review EGR 252.001 Spring 2009 Slide 1

Basic Probability Calculations

Cafeteria Method Multiplication rule

General Assignment Method Combinations

Specific Assignment Method Permutations

Partitioning Method Permutations

JMB Chapter 2 c Review EGR 252.001 Spring 2009 Slide 2

Cafeteria Problems

Pick one from each menu to define a single combination

Assuming you must pick one from each category, you apply the multiplication rule

Example: How many orders are possible if you select from 5 entrees, 3 desserts, and 2 drinks?

5*3*2 = 30 orders There are 30 different ways to make an order.

JMB Chapter 2 c Review EGR 252.001 Spring 2009 Slide 3

General Assignment Problems

Selections of subsets without regard to order Example: How many ways can we select 3

different books from a set of 12 different books? Example: How many ways can we assign 5

different teachers to participate in a summer training program if there are 2 openings?

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JMB Chapter 2 c Review EGR 252.001 Spring 2009 Slide 4

Specific Assignment Problems

How many ways can we assign 3 students to position of president, vice president or secretary if there are six people in the club? (n = 6, r = 3), permutations

Example: Five different teachers are available to teach EGR 252 and EGR 312 this term. In how many ways can we staff the courses if each teacher is only allowed to teach one course? (n = 5, r = 2), permutations

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JMB Chapter 2 c Review EGR 252.001 Spring 2009 Slide 5

Partitioning Problems

Example 2.20

In how many ways can we assign 7 students to one triple and two double rooms during a conference?

(n = 7, n1 = 3 n2 = 2 n3 = 2), 210 permutations Note that there are three partitions and the total number of partitions

(beds) available (n1+n2+n3) = the total number of students to be assigned (n).

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