QA 23

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course mth 151

If your solution to stated problem does not match the given solution, you should self-critique per instructions at

http://vhcc2.vhcc.edu/dsmith/geninfo/labrynth_created_fall_05/levl1_22/levl2_81/file3_259.htm

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Your solution, attempt at solution. If you are unable to attempt a solution, give a phrase-by-phrase interpretation of the problem along with a statement of what you do or do not understand about it. This response should be given, based on the work you did in completing the assignment, before you look at the given solution.

003. Intersection, Union, Complement, de Morgans Laws

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Question: `q001. Note that there are 6 questions in this assignment.

Again we have a total of 35 people in a room. Of these, 20 have dark hair and 15 have bright eyes. There are 8 people with dark hair and bright eyes.

Let A stand for the collection of people who have dark hair and B for the collection who have bright eyes. The Intersection of these two collections is denoted A ^ B, and stands for the collection of all people who have both dark hair and bright eyes. The Union of these two collections is denoted A U B, and stands for the collection of all people who have at least one of these characteristics.

In terms of the diagram you made for the preceding problem, describe the collection A ^ B and the collection A U B. Give the number of people in each of these collections (these numbers are designated by the notation n ( A ^ B) and n(A U B) ). Refer to the diagrams you have made.

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Your solution:

A=20 which is the dark haired people and B=15 which is the bright eyed people so region II would be 12 and region III would be 7 and region I is 8,so add all 3 regions 12+8+7=27 so this would make U=8 (the overlapping) (A^B)=8.so this leaves 8 people that do not have bright eyes or dark hair in the room.

confidence rating #$&*:

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Given Solution:

The collection A ^ B consists of all the people with both dark hair and bright eyes, which corresponds to the overlap between the two circles (region I). There are 8 people in this overlap, so we say n(A ^ B) = 8.

The collection A U B consists of all the people who have least one of the characteristics. This would include the 12 people with dark hair but not bright eyes, located in the first circle but outside the overlap (region II); plus the 7 people with bright eyes but not dark hair, located in the second circle but outside the overlap (region III); plus the 8 people with both characteristics, located in the overlap (region I). Thus we include the 12 + 8 + 7 = 27 people who might be located anywhere within the two circles.

The figure below, also seen in the QA for Assignment 2, represents this situation

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Self-critique (if necessary):

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Self-critique Rating:

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Question: `q002. Continuing the preceding example, we let A' stand for the people who are not in the collection A, and we let B' stand for the people who are not in the collection B.

What are the characteristics of the people in A', and what characterizes people in B' ? What are n(A ') and n(B '), the numbers of people in A' and B' ?

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Your solution: If A’ all the are all the people not in collection A(people with dark hair) so take the bright eyed people which is 7 and the amount outside the circle 8 so that make A’=7+8=15 Then B’= all the people who not in B (bright eyed people) so take the total of the dark hair people which is 12 and add the amount outside the circle 8, so B’=12+8=20

confidence rating #$&*:

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Given Solution:

Of the 35 people, those in A' are those outside of A. Since A consists of all the dark-haired people, A' consists of all the people lacking dark hair. This includes the 8 people outside of both circles (people having neither dark hair nor bright eyes, region IV) and the 7 people in the second circle but outside the overlap (people having bright eyes but not dark hair, region III). n(A ' ) is therefore 8 + 7 = 15.

Since B consists of all the bright-eyed people, B' consists of all the people lacking bright eyes. This would include the 8 people outside both circles (region IV), all of whom lack both dark hair and bright eyes, and the 12 people in the first circle but outside the overlap (region II), who have dark hair but not bright eyes. n ( B ' ) is therefore 12 + 8 = 20.

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Self-critique (if necessary):

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Question: `q003. ( A U B ) ' stands for the everyone outside A U B, and ( A ^ B ) ' stands for everyone outside A ^ B. What characterizes the people in each of these collections, and how many people are there in each?

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Your solution:

A U B is everyone that has at least one the characteristics (dark hair or bright eyes) would be region I,II, and III which is a total of 12+8+7=27, (AUB)’ would be the people who do not have any of the characteristics which would region IV which is 8 people. A^B stands for the people in region I with the overlapping of having both characteristics of dark hair and bright eyes which is 8, and (A^B)’ would be everyone that is not in the overlapping(region I) which would have dark hair or bright eyes or neither and this consist of 12+7+8=27 people.

confidence rating #$&*:

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Given Solution:

A U B consists of everyone having at least one of the characteristics (dark hair, bright eyes), and is represented by the numbers in the two circles (regions I, II, III). ( A U B ) ' consists of the people who do not have at least one of the characteristics, and is represented by the number outside both circles (region IV). This number is 8, representing the 8 people who have neither dark hair nor bright eyes.

A ^ B stands for all the people with both of the two characteristics (represented by the overlap, region I), so ( A ^ B ) ' stands for all the people who do not have both of the two characteristics (represented by everything outside region I, or regions II, III and IV). [ Note that (A ^ B)' is not the same as the collection of people who have neither characteristic. Anyone who does not have both characteristics will be in ( A ^ B ) ' . ] ( A ^ B )' must include those who have neither characteristic, and also those who have only one of the characteristics.

The 8 people outside both circles, the 12 people in the first circle but outside the overlap, and the 7 people in the second circle but outside the overlap all lack at least one characteristic to, so these 8 + 12 + 7 = 27 people make up( A ^ B ) '.

In the figure below:

AU B includes every region in the figure below that is part of A, as well as every region that is part of B. This description is true of every region I, II and III.

The only region not in A U B is region IV, so (A U B) ' consists of region IV.

A ^ B includes those regions which are both part of A and part of B. The only such region is Region I.

None of the regions II, III and IV can be said to be part of A as well as part of B. Thus ( A ^ B) ' consists of these three regions.

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Self-critique (if necessary):

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Self-critique Rating:

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Question: `q004. How many people are in A ' U B ', and how could those people be characterized? Answer the same for A ' ^ B '.

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Your solution:

A’UB’= the people in region II,III and IV which is 12+7+8=27 these are A’ is 7 and B’ is 12 and then region Iv which is 8-12+8+7=27 these are the people who have one or the other of the characteristics or neither.

confidence rating #$&*:

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Given Solution:

A ' U B ' consists of all the people who are in at least one of the sets A ' or B '.

A ' consists of all the people who do not have dark hair, represented by every region of the diagram which does not include any of A. This will include the 7 people in B who are outside the overlapping region, and the 8 people who are outside of both A and B (regions III and IV. Since A consists of regions I and II, A' consists of regions III and IV). B ' consists of all the people who do not have bright eyes, represented by every region of the diagram which does not include any of B (regions II and IV). This will include the 12 people in A but outside the overlap, and the 8 people outside of both A and B. Thus A ' U B ' consists of everyone in at least one of A ' or B ', including the 7 people in B but outside the overlap (region III), the 12 people in A let outside the overlap (region II), and the 8 people outside of both A and B (region IV). These will be the people who lack at least one of the characteristics dark hair and/or bright eyes.

Thus n(A' U B') = 7 + 12 + 8 = 27. Note that these are the same 27 people who are in ( A ^ B ) '. So at least in this case, ( A ^ B ) ' = A ' U B '.

A ' ^ B ' consists of all the people in both A ' and B '. As before A ' includes the 7 people in B but not A (region III) as well as the 8 people outside both A and B (region IV), and B ' includes the 12 people in A but not B (region II) as well as the 8 people outside both A and B (region IV). The people in both A ' and B ' will be the 8 people outside both A and B, those who have neither dark hair nor bright eyes.

We note that this is the same as the set ( A U B ) ', so at least for the present case we see that ( A ' ^ B ' = ( A U B ) '.

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Self-critique (if necessary):

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Question: `q005. Succinctly describe the relationships between ( A U B ) ', A ' U B ', (A ^ B) ' and A ' ^ B '.

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Your solution:

(AUB)’ is having neither characteristics of dark hair or bright eyes.

confidence rating #$&*:

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Given Solution:

( A U B ) ' = A ' ^ B ' and ( A ^ B ) ' = A ' U B '. The collection outside of the union A U B is the intersection A ' ^ B ', and the collection outside the intersection A ^ B is the union A ' U B '. The ' operation changes union to intersection and intersection to union.

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Self-critique (if necessary):I really did not understand how to do this problem. It seems as everything is all mixing together. I am Lost.

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Take this one step at a time.

Do you understand based on preceding questions that

( A U B ) ' = A ' ^ B ' ?

If not, what parts of the preceding questions were asking about sets that could be described as ( A U B ) ' , and about sets of the form A ' ^ B ' ?

Why was it that those sets were equal?

You can approach the equality

( A ^ B ) ' = A ' U B '

in a similar manner.

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Question: `q006. Suppose there are 200 people in a hall, 140 having dark hair, 90 having short hair and 50 having hair which is neither dark nor short. Let A be the set of people with dark hair, B the set of people with short hair.

Describe each of the following sets, indicate how many people are in each and explain how you got each result:

A ' ^ B

A U B '

(A ^ B) '

(A U B) '

(A 'U B ' ) '

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Your solution:

A’ ^ B- would be only the people with short hair

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jAll these people would have short hair, since they all must be in set B, but they must also be in set A ' so they would not have dark hair.

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A U B’-would be the people with dark hair and dark short hair which is 90+20=110

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Anybody in set A would be included, so all 140 people with dark hair would be included. So would all the people in B ', which would be the people whose hair is not short.

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(A ^ B)’- this would be the people with neither=50

(A U B)’-this would be the with neither=50

(A’ U B’)’-this would be people in A and B which is 90+40=130

confidence rating #$&*: very sure in these answers like I said before I got really confused.

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Self-critique (if necessary):

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Self-critique (if necessary):

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#*&!

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You do have a little confusion but you are thinking about the right things. Check my notes.

You will move on to the explanations in the text, which should clarify these ideas. Having worked through the text section you might (or might not) find it worth your time to revisit some of this document and see what you missed on your first encounter with these questions.

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