A First Course in Probability 10th Edition Solution Manual
Problems Chapter 1

1. (a) By the generalized basic principle of counting there are
   26  26  10  10  10  10  10 = 67,600,000
   (b) 26  25  10  9  8  7  6 = 19,656,000
2. 6
   4 = 1296
3. An assignment is a sequence i1, …, i20 where ij is the job to which person j is assigned. Since
   only one person can be assigned to a job, it follows that the sequence is a permutation of the
   numbers 1, …, 20 and so there are 20! different possible assignments.
4. There are 4! possible arrangements. By assigning instruments to Jay, Jack, John and Jim, in
   that order, we see by the generalized basic principle that there are 2  1  2  1 = 4 possibilities.
5. There were 8  2  9 = 144 possible codes. There were 1  2  9 = 18 that started with a 4.
6. Each kitten can be identified by a code number i, j, k, l where each of i, j, k, l is any of the
   numbers from 1 to 7. The number i represents which wife is carrying the kitten, j then
   represents which of that wife’s 7 sacks contain the kitten; k represents which of the 7 cats in
   sack j of wife i is the mother of the kitten; and l represents the number of the kitten of cat k in
   sack j of wife i. By the generalized principle there are thus 7  7  7  7 = 2401 kittens
7. (a) 6! = 720
   (b) 2  3!  3! = 72
   (c) 4!3! = 144
   (d) 6  3  2  2  1  1 = 72
8. (a) 5! = 120
   (b) 7!
   2!2!
   (c) 11!
   = 1260
   = 34,650
   4!4!2!
   (d) 7!
   2!2!
   = 1260
9. (12)!
   = 27,720
   6!4!
   1

2
5

5


5
5 5

2
    
2
2
Chapter 1

12. 103 − 10  9  8 = 280 numbers have at least 2 equal values. 280 − 10 = 270 have exactly 2
    equal values.
13. With ni equal to the number of length i, n1 = 3, n2 = 8, n3 = 12, n4 = 30, n5 = 30, giving the
    answer of 83.
14. (a) 305
    (b) 30  29  28  27  26
    15.
    16.
     20
     
     
    52
     
     
15. There are 1012
    possible choices of the 5 men and 5 women. They can then be paired up
      
    in 5! ways, since if we arbitrarily order the men then the first man can be paired with any of
    the 5 women, the next with any of the remaining 4, and so on. Hence, there are
    possible results.
    10 12 
    5!  
      
16. (a)
     6
    +
    7
    +
     4
    = 42 possibilities.
         
    (b) There are 6  7 choices of a math and a science book, 6  4 choices of a math and an
    economics book, and 7  4 choices of a science and an economics book. Hence, there are
    94 possible choices.
17. The first gift can go to any of the 10 children, the second to any of the remaining 9 children,
    and so on. Hence, there are 10  9  8    5  4 = 604,800 possibilities.
    2
18. (a) 8! = 40,320
    (b)
    (c)
    (d)
    2  7! = 10,080
    5!4! = 2,880
    4!24 = 384
19. (a) 6!
    (b) 3!2!3!
    (c) 3!4!

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2
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2

3
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
3

3
    
3
1 2

3

3
    
1
2 3
3 3 3 1 2

3

3
      
2
3 3 2

3

3


2

3

3 2

5
       
1
4 5 3
 
 
Chapter 1 3

20.  5  6  4 
    = 600
       
21. (a) There are 8 4
    +
    8 2 4
          
    = 896 possible committees.
    There are
    8 4
    that do not contain either of the 2 men, and there are 8 2 4
    that
      
      
    contain exactly 1 of them.
    (b) There are  66
    +
     2 66
    = 1000 possible committees.
          
       
       
    (c) There are
     75
    +
     75
    +
     75 
            
    = 910 possible committees. There are  75
    in
      
    which neither feuding party serves;
    75
    in which the feuding women serves; and
      
     7  5
      
      
    in which the feuding man serves.
22.  6
    +
     2 6
    ,
     6
    +
     6
            
23. 7!
    3!4!
    = 35. Each path is a linear arrangement of 4 r’s and 3 u’s (r for right and u for up). For
    instance the arrangement r, r, u, u, r, r, u specifies the path whose first 2 steps are to the right,
    next 2 steps are up, next 2 are to the right, and final step is up.
24. There are
    4!
    2!2!
    paths from A to the circled point; and 3!
    2!1!
    paths from the circled point to B.
    Thus, by the basic principle, there are 18 different paths from A to B that go through the
    circled point.
25. 3!23
26. (a)
    n
     n 
    2
    k = (2 +1)
    n
    k=0
    
    k
    
    (b) 
    n  n
    x
    k
    = ( x +1)
    n
    k=0 
    k
    

 
 
 
 

3


3
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
5 
5 5
4 Chapter 1

28.  52 
    
    13,13,13,13

30.  12 

12!

3, 4, 5

3!4!5!

31. Assuming teachers are distinct.
    (a) 4
    8
    (b) 

8 

8! = 2520.

2,2,2,2

(2)4

32. (a) (10)!/3!4!2!
    (b) 3
    3  7!
    
    2
    
    4!2!
33. 2  9! − 2
    28! since 2  9! is the number in which the French and English are next to each other
    and 228! the number in which the French and English are next to each other and the U.S. and
    Russian are next to each other.
34. (a) number of nonnegative integer solutions of x1 + x2 + x3 + x4 = 8.
    Hence, answer is 11
     
    = 165
    (b) here it is the number of positive solutions—hence answer is 7
    = 35
     
35. (a) number of nonnegative solutions of x1 + … + x6 = 8
    answer =
    13
     
    (b) (number of solutions of x1 + … + x6 = 5)  (number of solutions of x1 + … + x6 = 3) =
    108 
      
      