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Section 7.1: LOGIC Proposition:_____________________________________________________________ We use lowercase letters p,q,and r to denote propositions Compound propositions:
p¬ means “not p” (negation) p q∨ means “p or q” (disjunction) p q∧ means “p and q” (conjunction) p q→ means “if p then q” (conditional)
T* is called vacuously true
Think of a conditional as a guarantee like: “If you score at least 90%, then you will get an A”. Even if you score less than a 90%, the guarantee still remains in effect. 1. Consider the propositions p and q: p: “ 214 200< ” q: “ 223 500< ” Express each of the following propositions in an English sentence, and determine whether it is true or false. (A) p¬ ___________________________________________________________________________ (B) q¬ ___________________________________________________________________________ (C) p q∨ _________________________________________________________________________ (D) p q∧ _________________________________________________________________________ (E) p q→ ________________________________________________________________________ Let p q→ be a conditional proposition.
q p→ is called the converse of p q→ p q¬ →¬ is called the inverse of p q→ q p¬ →¬ is called the contrapositive of p q→
2. Consider the propositions p and q: p: “ 2 2 25 12 13+ = ” q: “ 2 2 27 24 25+ = ” Express each of the following propositions in an English sentence, and determine whether it is true or false. (A) p q→ _________________________________________________________________________ (B) The converse of p q→ ____________________________________________________________ (C) The inverse of p q→ _____________________________________________________________ (D) The contrapositive of p q→ _______________________________________________________
p q p¬ p q∨ p q∧ p q→
T T F T T T T F F T F F F T T T F T* F F T F F T*
Section 7.1: Logic Truth Tables – the first 2 columns of a truth table will always be p and q. P will be assigned the values TTFF respectively, and q will be assigned the values TFTF respectively to include all possible combinations. The remaining columns will be filled in with T or F according to their truth values. 3. Construct the truth table for p q∧¬
p q q¬ p q∧¬
T T
T F
F T
F F
4. Construct the truth table for ( )p q q p→ ∧¬ →¬⎡ ⎤⎣ ⎦
A proposition is called a __________________ if each entry in its column is a T A proposition is called a __________________ if each entry in its column is an F A proposition is called a __________________ if at least one each entry is a T and at least one entry is an F 5. Construct the truth table for ( ) ( )p q p q→ ∧ ∧¬
p q p q→ q¬ p q∧¬ ( ) ( )p q p q→ ∧ ∧¬
T T
T F
F T
F F
p q p q→ q¬ ( )p q q→ ∧¬ p¬ ( )p q q p→ ∧¬ →¬⎡ ⎤⎣ ⎦
T T
T F
F T
F F
Section 7.1: Logic If 2 compound propositions have the same truth values in their columns(T only, not F) then we can say the first propositions logically implies the second proposition and write p q⇒ . We callP Q⇒ a logical implication. 6. Show that ( ) ( )p q p q p→ → ⇒ →⎡ ⎤⎣ ⎦ p q p q→ ( )p q p→ → q p→
T T
T F
F T
F F
Now compare the 4th and 5th columns. Whenever ( )p q p→ → is true (1st two rows), q p→ is also
true. We therefore conclude that ( ) ( )p q p q p→ → ⇒ →⎡ ⎤⎣ ⎦ If two compound propositions have identical truth tables (T&F), then they are logically equivalent and can be written P Q≡ . We call P Q≡ a logical equivalence. Some logical equivalences: 1 ( )p p¬ ¬ ≡
2 p q q p∨ ≡ ∨
3 p q q p∧ ≡ ∧
4 p q p q→ ≡ ¬ ∨
5 ( )p q p q¬ ∨ ≡¬ ∧¬
6 ( )p q p q¬ ∧ ≡¬ ∨¬
7 p q q p→ ≡ ¬ →¬
7. Show that ( )p q p q¬ ∧ ≡¬ ∨¬ p q p q∧ ( )p q¬ ∧ p¬ q¬ p q¬ ∨¬
T T
T F
F T
F F
The 4th and 7th columns are identical, so ( )p q p q¬ ∧ ≡¬ ∨¬
Section 7.2: SETS Set: __________________________________________________________________________________________________________ Capital letters such as A, B, and C are used to designate sets. Each object in a set is called an ________________ of the set. a A∈ means “a is an element of set A” a A∉ means “a is not an element of set A” A set without any elements is called the ___________, or ____________ set. For example, the set of all people over 20 feet tall is an empty set. Symbolically, ∅ denotes the empty set. A set is described by either (1) listing all of its elements between braces {} or by (2) writing a rule within braces that determines the elements of the set. Rule Listing Examples: {x| x is a weekend day} {Saturday, Sunday} {x| 2 4x = } {2, -‐2} {x| x is a positive odd counting number} {1,3,5,…} The three dots in the last set indicate that the pattern established by the first 3 entries continues indefinitely. The first 2 sets are called finite sets(countable), the 3rd set is an infinite set. 1. Let G be the set of all numbers such that 2 9x = (A) Denote G by the rule method __________________________ (B) Denote G by the listing method __________________________ (C) Indicate whether the following are true or false: 3 G∈ ______ 9 G∉ ______ If each element in set A is also in set B then we call set A a ______________ of set B. For example, the set of all girls in the class is a subset of the whole class. If set A and set B have exactly the same elements, then the two sets are said to be equal. Symbolically, A B⊂ means “A is a subset of B” A B= means “A & B have exactly the same elements” A B⊄ means “A is not a subset of B” A B≠ means “A & B do not have exactly the same elements” *From the definition of subset, we can conclude that ∅ is a subset of every set.* 2. Given A={0,2,4,6}, B={0,1,2,3,4,5,6}, and C={2,6,0,4}, indicate whether the following relationships are true (T) or false (F):
(A) A B⊂ _____ (B) A C⊂ _____ (C) A C= _____
(D) C B⊂ _____ (E) B A⊄ _____ (F) B∅⊂ _____ 3. List all the subsets of the set {1,2}
Section 7.2: Sets SET OPERATIONS The union of sets A and B, denoted by A B∪ is the set of all elements formed by combining all the elements of set A and all of the elements of set B into one set. Symbolically: { }| orA B x x A x B∪ = ∈ ∈ The union of 2 sets can be illustrated using a Venn Diagram: A B The intersection of set A and B, denoted by A B∩ , is the set of elements in set A that are also in set B. Symbolically: { }| andA B x x A x B∩ = ∈ ∈ The intersection of 2 sets can be illustrated using a Venn Diagram: A B If sets A and B have no elements in common, ( A B∩ =∅ ), they are said to be disjoint. The set of all elements under consideration in called the universal set U. The complement of A, denoted by A’, is the set of elements in U that are not in A. Symbolically: { }' |A x U x A= ∈ ∉ U A A’ 4. If { }1,2,3,4R = , { }1,3,5,7S = , { }2,4T = , and { }1,2,3,4,5,6,7,8,9U = , find (A) R S∪ _________________________ (C) S T∩ _________________________ (B) R S∩ _________________________ (D) 'S _________________________ 5. In a survey of 100 randomly chosen students, a marketing questionnaire included the following 3 questions: (1) Do you own a TV? (2) Do you own a car? (3) Do you own a TV and a car? 75 students answered yes to question 1, 45 students answered yes to question 2,
35 students answered yes to question 3 Make a Venn diagram to aid in this problem. U = set of students in sample _____ U T C T = set of students who own TV sets _____ C = set of students who own cars _____ T C∩ = set of students who own cars & TV sets _____ (A) How many students owned either a car or TV? ______ (B) How many students did not own either a car or TV? ______ (C) How many students owned a car but not a TV? ______ (D) How many students did not own both a car and TV? ______
Section 7.3: BASIC COUNTING PRINCIPLES The number of elements in a set A is denoted by n(A) Sets A and B are called _______________ if A B∩ =∅ Addition Principle for Counting: For any 2 sets A and B, ( ) ( ) ( ) ( )n A B n A n B n A B∪ = + − ∩ If A and B are disjoint, then ( ) ( ) ( )n A B n A n B∪ = + 1. According to a survey of business firms in Cypress, 345 firms offer their employees group life insurance, 285 offer long-‐term disability insurance, and 115 offer group life insurance and long-‐term disability insurance. How many firms offer their employees group life insurance or long-‐term disability insurance? SOLUTION: If G = set of firms that offer employees group life insurance, and D = set of firms that offer employees long-‐term disability insurance, then G D∩ = set of firms that offer group life insurance and long-‐term disability insurance G D∪ = set of firms that offer group life insurance or long-‐term disability insurance Thus, n(G) = _____ n(D) = _____ n(G D∩ ) = _____ and ( ) ( ) ( ) ( )n G D n G n D n G D∪ = + − ∩ = ______ + _____ -‐ _____ = _____ 2. A small town has 2 radio stations, an AM station and an FM station. A survey of 100 residents of the town produced the following results: In the last 30 days, 65 people have listened to the AM station, 45 people have listened to the FM station, and 30 have listened to both stations. (A) How many people in the survey have listened to the AM station but not to the FM station? _____ (B) How many have listened to the FM station but not to the AM station? _____ (C) How many have not listened to either station? _____ (D) Organize this information in a table. Let U = the group of people surveyed Let A = set who listened to AM station Let F = set who listened to FM station U A F 'A F∩ A F∩ 'A F∩ _____ _____ _____ ' 'A F∩ ______
FM Listener FM Non Total
AM Listener
AM Non
Total
Section 7.3: Basic Counting Principles Multiplication Principle for Counting: If two operations, 1O and 2O are performed in order, where
1O has 1N possible outcomes and 2O has 2N possible outcomes, then there are N1iN2 possible outcomes of the first operation followed by the second. In general, if n operations 1O , 2O , … nO are performed in order, with possible number of outcomes
1N , 2N , … nN respectively, then there are N1iN2 i...iNn possible combined outcomes of the operations performed in the given order. 3. An Apple store stocks 4 types of ipod: ipod 8G , ipod 16G, mini, and nano. They are low on stock and are only available in blue and red. What are the combined choices, and how many combined choices are there? Solve using a tree diagram.
iPod OPTIONS COLOR COMBINED CHOICES 4. If we had asked: “From the 26 letters of the alphabet, how many ways can 3 letters appear in a row on a license plate so no letter is repeated?”, it would be tedious to list the possibilities in a tree diagram so we would use the multiplication counting principle to solve this problem. What would the answer be? 5. Each question on your multiple choice computer work has 4 choices. There are 20 questions on this week’s work. How many different combinations of answers exist for the 20 questions? 6. How many 4-‐letter code words are possible using the first 10 letters of the alphabet if:
(A) No letter can be repeated? (B) Letters can be repeated? (C) Adjacent letters cannot be alike?
Section 7.4: PERMUTATIONS & COMBINATIONS FACTORIALS The product of the first n natural numbers is called n factorial and is denoted n! n! = n(n-‐1)(n-‐2)…(2)(1) ex: 6! = 6x5x4x3x2x1 = 720 n! = n(n-‐1)! 0! = 1 your calculator should have a factorial button on it -‐-‐> n! 1. Use your calculator to compute each factorial expression.
(A) 5! (B) 10!9! (C) 10!
7! (D) 5!
0!3! (E) 20!
3!17!
n! grows very rapidly. What is the highest factorial value your calculator can find? PERMUTATIONS A permutation of a set of objects is an arrangement of the objects in a specific order without repetition. 2a. Suppose 5 pictures are to be arranged from left to right on the wall of an art gallery. How many permutations (ordered arrangements) are possible? The number of permutations of n distinct objects without repetition is n! 2b. Now suppose the art gallery only has room for only 3 of the 5 pictures and they will be arranged on the wall from left to right. This is a permutation of 5 objects taken 3 at a time. It is denoted P5,3 In general, a permutation of a set of n objects taken r at a time without repetition is denoted Pn,r and
is given by: Pn,r =n!
n − r( )! where 0 ≤ r ≤ n
So for our art gallery problem P5,3 =__!
__− __( )! =__!__!
=__⋅ __⋅ __⋅ __⋅ __
__⋅ __= __⋅ __⋅ __ = ___
Section 7.4: Permutations & Combinations 3. Given the set {A,B,C,D}, how many permutations are there of this set of 4 objects taken 2 at a time? Answer the questions (A) Using a tree diagram (B) Using the multiplication principle (C) Using the formula for permutations.
(A) (B) (_____)(_____)
(C) P4,2 =__!
__− __( )! =
COMBINATIONS A combination of a set of n distinct objects taken r at a time without repetition is an r-‐element subset of the set of n objects. The arrangement of the elements in the subset does not matter. 4. How many ways can 3 paintings be selected for shipment out of the 8 paintings available? This is the same thing as the number of combinations of 8 objects taken 3 at a time.
Using the Combination formula: Cn,r =n!
r! n − r( )! where 0 ≤ r ≤ n
5. Find the number of permutations of 30 objects taken 4 at a time.
P30,4 =__!
__− __( )! =
6. Find the number of combinations of 30 objects taken 4 at a time.
Section 7.4: Permutations & Combinations 7. From a committee of 12 people,
(A) In how many ways can we choose a chairperson, a vice-‐chairperson, a secretary, and a
treasurer, assuming that one person cannot hold more than one position?
(B) In how many ways can we choose a subcommittee of 4 people? 8. In a standard 52-‐card deck, how many 5-‐card hands will have 3 hearts and 2 spades? 9. Serial numbers for a product are to be made using 3 letters followed by 2 numbers. If the letters are to be taken from the first 8 letters of the alphabet with no repeats and the numbers are to be taken from the 10 digits (0 – 9) with no repeats, how many serial numbers are possible? (Order is important) 10. A company has 7 senior and 5 junior officers. A safety committee is to be formed. In how many ways can a 4-‐officer committee be formed so that it is composed of (a) 1 senior officer and 3 junior officers? (b) 4 junior officers? (c) at least 2 junior officers?