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MATH260Ch. 5: Probability Theorypart 4Counting: Multiplication, Permutations, Combinations

Permutation Examples
1. If there are 4 people in the math club (Anne,Bob,Cindy,Dave), and we wish to elect a president and vice-president, LIST all of the different ways that this is possible.2. From these 4 people (Anne,Bob,Cindy,Dave), we wish to elect a president, vice-president, and treasurer. LIST all of the different ways that this is possible.
Answers
1. If there are 4 people in the math club (Anne,Bob,Cindy,Dave), and we wish to elect a president and vice-president, LIST all of the different ways that this is possible.AB BA CA DAAC BC CB DBAD BD CD DC4*3=12 or 4P2 = 12
Answers
2. From these 4 people (Anne,Bob,Cindy,Dave), we wish to elect a president, vice-president, and treasurer. LIST all of the different ways that this is possible.ABCABD…

A B C ABCD ABDC B ACBD ACDD A BDAC BDCB A C BACD BCDC A BCAD BCDD A BDAC BDCC A B CABD CADB A CBAD CBDA B DABC DACD A B DABC DACB A DBAC DBCC A DCAB DCB4*3*2 = 24 outcomesOr 4P3 = 24
More counting examples:
1.      At a restaurant, you have a choice of main dish (beef, chicken, fish, vegetarian), vegetable (broccoli, corn), potato (baked, fries), and dessert (chocolate, strawberry).  LIST all possible choices.
2. T/F quiz
2.      A teacher wishes to make all possible different answer keys to a T/F quiz to cut down on cheating.  How many possible different answer keys could there be if there are 4 questions.  LIST them all.
3. T/F test
3.      What if there were 10 T/F questions.  Just explain (do not list).
4. Multiple choice test
4.      A teacher wishes to make all possible different answer keys to a multiple choice quiz.  How many possible different answer keys could there be if there are 3 questions that each have 4 choices (A,B,C,D).  LIST them all.
5. And 6.
5.      What if there were 20 multiple choice questions with 5 choices each? Explain (don’t list).6.      With 9 baseball players on a team, how many different batting orders exist?
Counting Rules
Fundamental Counting/ –Multiplication Rule (p. 608)If you can choose one item from a group of M items and a second item from a group of N items, then the total number of two-item choices is M*N.Permutation of n things taken r at a time (p. 617)nPr=     n!/(n-r)!In permutations, ORDER matters & REPETITION is NOT allowed?Permutations of Duplicate items (p. 618)The number of permutations of n items, where p items are identical, q items are identical, r items are identical, and so on, is given by
More multiplication and permutation problems
1.      With 14 players on a team, how many ways could we pick a batting order of 11?2.      If license plates have 3 letters and then 4 numbers, how many different license plates exist?
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3.      A stock can go up, down, or stay unchanged.  If you own 7 stocks, how many different possibilities are there?
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4.      How many different four-letter radio station call letters can be formed if the first letter must be W or K?5.      A social security number contains nine digits.  How many different ones can be formed?
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6.      If you wish to arrange your 7 favorite books on a shelf, how many different ways can this be done?7.      If you have 10 favorite books, but only have room for 7 books on the shelf, how many ways can you arrange them?
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8.      You wish to arrange 12 of your favorite photographs on a mantel.  How many ways can this be done?9.      You have 20 favorite photographs and wish to arrange 12 of them on a mantel.  How many ways can that be done?
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10.  You take a multiple choice test with 12 questions (and each can be answered A B C D E).  How many different ways could you answer the test?
11.  How many ways can you rearrange the letters in
a.       CAT?b.      OHIO?c.       CLASSES?d.      MISSISSIPPI?
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12.  If a station plans on running 6 (identical) Democratic ads, 6 (identical) Republican ads, and 4 (identical) Independent ads, in how many ways can they order these?13.  If you saw 15 movies last year, how many ways can the top 3 be chosen and ranked?
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14.  20 people purchase raffle tickets.  How many ways could we award a 1st, 2nd, and 3rdprize.15.  You have 50 different outfits.  How many ways can you pick your first and second favorite? How about your first, second, and third favorite?
Combination Questions
If there are 4 people in the math club (Anne,Bob,Cindy,Dave), and 2 will be selected to attend the national math conference. LIST all of the different ways that this is possible.From these 4 people (Anne,Bob,Cindy,Dave), and 3 will be selected to attend the national math conference. LIST all of the different ways that this is possible.
Combination answers
1. If there are 4 people in the math club (Anne,Bob,Cindy,Dave), and 2 will be selected to attend the national math conference. LIST all of the different ways that this is possible.ABAC BCAD BD CD4C2= 6
Combination answer
2. From these 4 people (Anne,Bob,Cindy,Dave), and 3 will be selected to attend the national math conference. LIST all of the different ways that this is possible.ABC BCDABDACD4C3 = 4
Permutations and Combinations
PermutationsUse when ORDER matters and NO repetitionnPr= n!/(n-r)!Example: If 10 people join a club, how many ways could we pick pres andvp? 10P2 = 90CombinationsUse: ORDER does NOT matter and NO repetitionnCr= n!/ [(n-r)!r!]Example: 10 people join a club. In how many ways could we pick 2? 10C2 = 45
Combination of n things taken r at a time (p. 623)
Use the combination formulanCr= n!/[(n-r)!r!] to answer these combination problems1.      If there are 20 people on a committee, how many ways could we pick a subcommittee of 7 of them?2    If there are 100 senators, how many ways could we pick a subcommittee of 7 of them?3    If there are 72 potential jurors, how many different ways could they pick a jury of 12?
Decide and answer: Combination, permutation, or multiplication?
There are 8 possible pizza toppings.  How many ways could we pick 3 toppings?2 . 20 people apply for a scholarship.  3 are chosen.  In how many ways can they be chosen?3. 32 people are in a class where the teacher plans on awarding 4 A’s.  If all possibilities were written out, how many would there be?
Changesome of the following permutation problems into combination problems
1.      Permutation question: With 14 players on a team, how many ways could we pick a batting order of 11? Answer: 14P11Write a combination questions whose answer is 14C112.      Permutation question: If you have 10 favorite books, but only have room for 7 books on the shelf, how many ways can you arrangethem?Answer: 10P7Write a combination questions whose answer is 10C7

3.      Permutation question: You have 20 favorite photographs and wish to arrange 12 of them on a mantel.  How many ways can that be done? Answer: 20P12Write a combination questions whose answer is 20C124.  Permutation question: If you saw 15 movies last year, how many ways can the top 3 be chosen and ranked? Answer: 15P3Write a combination questions whose answer is 15C3

5.     Permutation question: 20 people purchase raffle tickets.  How many ways could we award a 1st, 2nd, and 3rdprize. Answer: 20P3Write a combination questions whose answer is 20C3
More challenging combination problems
1      If we have 4 teachers and 7 students and wish to form a committee of 2 teachers and 3 students, in how many different ways can this be done?

2 .  A test has 5 essay questions and 10 short answer questions. A student is to select to answer 3 essay questions and 7 short answers.   In how many different ways could this be done?
Review --Multiplication, Permutation, or Combination?
1. With 14 players on a team, how many ways could we pick a batting order of 11?2.      If license plates have 3 letters and then 4 numbers, how many different license plates exist?3.      How many different four-letter radio station call letters can be formed if the first letter must be W or K?4.      A social security number contains nine digits.  How many different ones can be formed?5.      If you wish to arrange your 7 favorite books on a shelf, how many different ways can this be done?

6.   If you have 10 favorite books, but only have room for 7 books on the shelf, how many ways can you arrange them?7.      You wish to arrange 12 of your favorite photographs on a mantel.  How many ways can this be done?8.      You have 20 favorite photographs and wish to arrange 12 of them on a mantel.  How many ways can that be done?9.  You take a multiple choice test with 12 questions (and each can be answered A B C D E).  How many different ways could you answer the test?10. If you had 13 pizza toppings, how many ways could you pick 5 of them?

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