Download Section 2.1-2.2 Sample space (p.38)

Section 2.1-2.2 Sample space (p.38)
2.4 (a) An experiment involves tossing a pair of dice, 1 green and 1 red, and
recording the numbers that come up. If x equals the outcome on the green die
and y the outcome on the red die, describe the sample space S by listing the
elements (x, y).
sol)
S = {(1, 1), (1, 2), (1, 3), (1, 4), (1, 5), (1, 6),
(2, 1), (2, 2), (2, 3), (2, 4), (2, 5), (2, 6),
(3, 1), (3, 2), (3, 3), (3, 4), (3, 5), (3, 6),
(4, 1), (4, 2), (4, 3), (4, 4), (4, 5), (4, 6),
(5, 1), (5, 2), (5, 3), (5, 4), (5, 5), (5, 6),
(6, 1), (6, 2), (6, 3), (6, 4), (6, 5), (6, 6)}
2.5 An experiment consists of tossing a die and then flipping a coin once if the
number on the die is even. If the number on the die is odd, the coin is flipped
twice. Using the notation 4H, for example, to denote the outcome that the die
comes up 4 and then the coin comes up heads, and 3HT to denote the outcome
that the die comes up 3 followed by a head and then a tail on the coin, construct
a tree diagram to show the 18 elements of the sample space S.
sol)
S = {1HH, 1HT, 1T H, 1T T, 2H, 2T, 3HH, 3HT, 3T H, 3T T, 4H, 4T, 5HH,
5HT, 5T H, 5T T, 6H, 6T }
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2.14 If S = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9} and A = {0, 2, 4, 6, 8}, B = {1, 3, 5, 7, 9},
C = {2, 3, 4, 5}, and D = {1, 6, 7}, list the elements of the sets corresponding to
the following events:
(a) A ∪ C
sol)
A ∪ C = {0, 2, 3, 4, 5, 6, 8}
(b) A ∩ B
sol)
A∩B =∅
(c) C 0
sol)
C 0 = {0, 1, 6, 7, 8, 9}
(d) (C 0 ∩ D) ∪ B
sol)
(C 0 ∩ D) ∪ B = {1, 6, 7} ∪ {1, 3, 5, 7, 9} = {1, 3, 5, 6, 7, 9}
0
(e) (S ∩ C)
sol)
0
(S ∩ C) = C 0 = {0, 1, 6, 7, 8, 9}
(f) A ∩ C ∩ D0
sol)
A ∩ C ∩ D0 = {0, 2, 4, 6, 8} ∩ {2, 3, 4, 5} ∩ {0, 2, 3, 4, 5, 8, 9} = {2, 4}
2.17 Let A , B , and C be events relative to the sample space S. Using Venn
diagrams, shade the areas representing the following events:
0
(a) (A ∩ B)
sol)
2
0
(b) (A ∪ B)
sol)
(c) (A ∩ C) ∪ B
sol)
Section 2.3 Counting (p.47)
2.22 In a medical study patients are classified in 8 ways according to whether
they have blood type AB + , AB − , A+ , A− , B + , B − , O+ , or O− , and also
according to whether their blood pressure is low, normal, or high. Find the
number of ways in which a patient can be classified.
sol)
With n1 = 8 blood types and n2 = 3 classifications of blood pressure, the multiplication rule gives n1 n2 = (8)(3) = 24 classifications.
2.30 In how many different ways can a true-false test consisting of 9 questions
be answered?
sol)
n1 = 2, n2 = 2, n3 = 2, n4 = 2, n5 = 2, n6 = 2, n7 = 2, n8 = 2, n9 = 2
By theorem 2.1, n1 n2 n3 n4 n5 n6 n7 n8 n9 = (2)(2)(2)(2)(2)(2)(2)(2)(2) = 29 = 512
possible ways.
2.31 If a multiple-choice test consists of 5 questions each with 4 possible answers of which only 1 is correct,
(a) In how many different ways can a student check off one answer to each
question?
sol)
3
n1 = 4, n2 = 4, n3 = 4, n4 = 4, n5 = 4
By theorem 2.1, n1 n2 n3 n4 n5 = (4)(4)(4)(4)(4) = 45 = 1024 possible ways.
(b) In how many ways can a student check off one answer to each question
and get all the answers wrong?
sol)
n1 = 3, n2 = 3, n3 = 3, n4 = 3, n5 = 3
By theorem 2.1, n1 n2 n3 n4 n5 = (3)(3)(3)(3)(3) = 35 = 243 possible ways.
2.33 A witness to a hit-and-run accident told the police that the license number
contained the letters RLH followed by 3digits, the first of which is a 5. If the
witness cannot recall the last 2 digits, but is certain that all 3 digits are different, find the maximum number of automobile registrations that the police may
have to check.
sol)
n1 = 9 (since all possible numbers are 0, 1, 2, 3, 4, 6, 7, 8, 9), n2 = 8 (= n1 − 1)
By theorem 2.1, n1 n2 = (9)(8) = 72
2.37 In how many ways can 4 boys and 5 girls sit in a row if the boys and
girls must alternate?
sol)
G indicates a girl’s sit.
B indicates a boy’s sit.
GBGBGBGBG
Girls can sit 5! different ways and boys can sit 4! different ways.
Thus, 5! × 4! = 2880 possible ways.
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