course Mth 151 ʆEQ胫 {ῤeaassignment #002
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14:20:37 2.2.24 U={a,b,...,g}, A={a,e}, B={a,b,e,f,g}, C={b,f,g}, D={d,e} Is C ps U? Is the statement true or false and why?
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RESPONSE --> True. C is a proper subset of U because each element of C is contained in U, but C does not contain every element of U. confidence assessment: 3
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14:20:54 ** It's true because all elements of C are in the universal set, and because there are elements of U that aren't in C. You have to have both conditions, since a proper subset cannot be identical to other set. **
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RESPONSE --> OK self critique assessment: 3
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14:21:17 Query 2.2.30 phi s D
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RESPONSE --> True. confidence assessment: 3
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14:21:41 ** Note that You should be responding to problem 2.2.30 from the homework you worked out on paper. The shorthand notation is for my reference and won't always make sense to you. For clarification, though, the symbol for the empty set is the Greek letter phi. One set is a subset of another if every element of that set is in the other. To show that a set isn't a subset of another you have to show something in that set that isn't in the other. There's nothing in the empty set so you can never do this--you can never show that it has something the other set doesn't. So you can never say that the empty set isn't a subset of another set. Thus the empty set is a subset of any given set, and in particular it's a subset of D. ALTERNATIVE ANSWER: As the text tells you, the empty set is a subset of every set. ANOTHER ALTERNATIVE Every element of the empty set is in D because there is no element in the empty set available to lie outside of D. ONE MORE ALTERNATIVE: The empty set is a subset of every set. Any element in an empty set is in any set, since there's nothing in the empty set to contradict that statement. **
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RESPONSE --> OK self critique assessment: 3
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14:22:18 2.2.33 D not s B Is the statement true or false and why?
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RESPONSE --> True. D is not a subset of B because D contains elements that are not in B. confidence assessment: 3
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14:22:30 ** D is a subset of B if every element of D is an element of B-i.e., if D doesn't contain anything that B doesn't also contain. The statement says that D is not a subset of B. This will be so if D contains at least one element that B doesn't. **
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RESPONSE --> OK self critique assessment: 3
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14:23:25 2.2.36 there are exactly 31 subsets of B
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RESPONSE --> False. There are 32 subsets of B. confidence assessment: 3
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14:23:32 ** If a set has n elements then is has 2^n subsets, all but one of which are proper subsets. B has 5 elements so it has 2^5 = 32 subsets. So the statement is false. There are exactly 31 proper subsets of B, but there are 32 subsets of B. **
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RESPONSE --> OK self critique assessment: 3
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14:25:03 Query 2.2.40 there are exactly 127 proper subsets of U Is the statement true or false and why?
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RESPONSE --> True. There are 7 elements in U. To find the total number of subsets you multiply 2 to the seventh power - to find the number of proper subsets, you subtract one from that number. 2 to the seventh power is 128, so there are 127 possible proper subsets. confidence assessment: 3
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14:25:12 ** The set is not a proper subset of itself, and the set itself is contained in the 2^n = 2^7 = 128 subsets of this 7-element set. This leaves 128-1 = 127 proper subsets. **
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RESPONSE --> OK self critique assessment: 3
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14:26:49 Query 2.2.48 U={1,2,...,10}, complement of {2,5,7,9,10} What is the complement of the given set?
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RESPONSE --> The complement of {2, 5, 7, 9, 10} is {1, 3, 4, 6, 8} confidence assessment: 3
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14:26:54 ** the complement is {1,3,4,6,8}, the set of all elements in U that aren't in the given set. **
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RESPONSE --> OK self critique assessment: 3
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14:27:35 query 2.2.63 in how many ways can 3 of the five people A, B, C, D, E gather in a suite?
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RESPONSE --> 10 possible ways confidence assessment: 3
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14:27:45 ** The answer here would consist of a list of all 3-element subsets: {a,b,c}, {a,b,d}, {a,b,e}, {a,c,d} etc. There are ten such subsets. Using a,b,c,d,e to stand for the names, we can list them in alphabetical order: {a,b,c), {a,b,d}, {a,b,e}, {a,c,d}, {a,c,e}, {a,d,e|, {b,c,d}, {b,c,e}, {b,d,e}, {c, d, e}**
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RESPONSE --> OK self critique assessment: 3
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