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Main points of this past exam are: Enjoy, Venn Diagram, Helping People, Sue, Invalid, Argument, Symbolic Statement
Typology: Exercises
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Solution: The argument is invalid. From the Venn dia- gram, we see Sue can enjoy helping while not being a politician.
Politicians
those who enjoy helping people
Sue
Solution: p q p → q (^) ˜ q → (^) ˜ p T T T T T F F F F T T T F F T T
The last two columns agree, so the statement p → q is logically equivalent to ˜ q → (^) ˜ p.
Solution: Use the symbolic representations p : a student studies regularly; q : the student does well in school; r : the student’s teachers are good. Then the paragraph can be written as ( (p → q) ∧ (r → q) ∧ ( ˜ q)
˜ p^ ∨^ ˜ r
which turns out to be a tautology, so the argument is valid. p q r p → q r → q (^) ˜ q (p → q) ∧ (r → q) ∧ ( ˜ q) (^) ˜ p ∨ (^) ˜ r paragraph T T T T T F F F T T T F T T T T T T T F T F F F F F T T F F F T T F T T F T T T T F T T T F T F T T T T T T F F T T F F F T T F F F T T T T T T
Solution: Statement (c) is the contrapositive of statement (b), so they are logically equivalent. Statement (b) is the converse of (a) so they aren’t equivalent.
Solution: Beginning with the universal set U , just delete all elements that are in A ∩ B to get (A ∩ B) ′^ = { b, d, e, f , g, h, i, l }. The Venn diagram for (A ∪ B) ′^ is shown to the right.
A B
U
Solution: We know that n(A ∪ B) = n(A) + n(B) − n(A ∩ B). Since we are given that 61 like neither, we know that 250 − 61 = 189 like at least one, so n(A ∪ B) = 189. So 189 = 164 + 128 − n(A ∩ B). Thus, n(A ∩ B) = 102.
63 102
61
Ba
ske tball Baseb all
24
Solution: Using the formulas we have 7 P 3 = (^) ( 7 −7! 3 )! = 7 · 6 · 5 = 210 and 7 C 3 = (^) ( 7 −7! 3 ) !3! = 73 ·^6 · 2 ·^5 = 35. For counting problems, you could say:
From a group of 7 people, we want to select 3 and line them up in a row (answer 7 P 3 ). From a group of 7 people, we want to select 3 to form a committee (answer 7 C 3 ).