QA 2

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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.

002. Representing Sets

Note that there are 3 questions in this assignment.

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Question: `q001. We can represent the collection consisting of the letters a, b, c, d, e, f by a circle in which we write these letters. If we have another collection consisting of the letters a, c, f, g, k, we could represent it also by a circle containing these letters. If both collections are represented in the same diagram, then since the two collections have certain elements in common the two circles should overlap.

Sketch a diagram with two overlapping circles. The two circles will create four regions. The first region is the region where the circles overlap. The second region is the one outside of both circles. The third region is the part of the first circle that doesn't include the overlap. The fourth region is the part of the second circle that doesn't include the overlap. Number these regions with the Roman numerals I (the overlap), II (first circle outside overlap), III (second circle outside overlap) and IV (outside both circles).

Let the first circle contain the letters in the first collection and let the second circle contain the letters in the second collection, with the letters common to both circles represented in the overlapping region.

Which letters, if any, go in region I, which in region II, which in region III and which in region IV?

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Your solution:

Region I- a,c,f

Region II- a,b,c,d,e,f,

Region III- a,c,f,g,k

Region IV- H,I,J,L,M,N,O,P,Q,R,S,T,U,V,W,X,Y,Z

confidence rating #$&*:3

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Given Solution:

The circles would appear and be labeled as below:

The letters a, c and f go in the overlapping region, which we called Region I. The remaining letters in the first collection are b, d, and e, and they go in the part of the first circle that does not include the overlapping region, which we called Region II. The letters g and k go in the part of the second circle that does not include the overlapping region (Region III). There are no letters in Region IV.

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Self-critique (if necessary): I included the letters the overlapped into their original sets as well. I suppose that was redundant, but I did what I did. I will remember not to in the future.

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Self-critique Rating:

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Question: `q002. Suppose that 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.

Draw two circles, one representing the dark-haired people and the other representing the bright-eyed people. Represent the dark-haired people without bright eyes by writing this number in the part of the first circle that doesn't include the overlap (region II). Represent the number of bright-eyed people without dark hair by writing this number in the part of the second circle that doesn't include the overlap (region III). Write the appropriate number in the overlap (region I).

How many people are included in the first circle, and how many in the second?

How many people are included in both circles?

How many of the 35 people are not included in either circle?

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Your solution:

Region I- 8 have both dark hair and bright eyes

Region II- Since 8 of the people included in the group of 20 people who have dark hair can also be included in the overlapping region, we can say that they would be subtracted from the main group, making this number to represent people with dark hair only to be 12

Region III- Using the same method of reasoning we can say that 15-8=7 making the number of people with Bright Eyes only is 7

Region IV- Since we have 12+8+7 included in the group, which comes to 27, we can assume the rest that makes up the total number of 35 to be in this outside region. Therefore, 35-27=8. So there are 8 people in this fourth region.

confidence rating #$&*:2

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Given Solution:

These numbers are represented in the circles below.

A number on the boundary of a circle indicates the total number in that circle, so the figure represents 20 individuals in circle A and 15 in circle B. The number 35 on the boundary of the entire figure represents the total number of individuals in the room, which in this case is 35.

A number inside one of the regions I, II, III, IV represents the number in that region. The 8 having both dark hair and bright eyes will occupy the overlap between the circles (region I).

Of the 15 people with bright eyes, 8 also have dark hair so the other 7 do not have dark hair, and this number will be represented by the part of the second circle that doesn't include the overlap (region III). This is indicated by the number 7 inside region III in the figure below.

Of the 20 dark-haired people in the preceding example, 8 also have bright eyes. This leaves 12 dark-haired people for that part of the circle that doesn't include the overlap (region II).

We have accounted for 12 + 8 + 7 = 27 people. This leaves 35-27 = 8 people who are not included in either of the circles. The number 8 can be written outside the two circles (region IV) to indicate the 8 people who have neither dark hair nor bright eyes, as is indicated by the number 8 in region IV in the figure below:

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Self-critique (if necessary): I was confused with this one as I assumed that I should have come to a number without anyone on the outside boundry, since the original problem described 15 people with bright eyes and 20 people with dark hair I had perceived all the people in question to be accounted as having either bright eyes or dark hair. Once I understood the fact that some of them may not have either trait then the problem was easy enough to figure out.

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Self-critique Rating:

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Question: `q003. 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. Sketch a diagram like the ones above, specify how many people are in each of the four regions and describe the people in each region.

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Your solution:

Region I- By adding all three given numbers from the problem we can see that we are in excess of 80

140+50+90=280

Since we only have 200 people total we can think that these extra 80 are there because they have been counted twice in the 2 differing groups in question. Further math which I will explain proves that there should be 80 people in the equation which have both dark and short hair.

Region II- This region represents dark haired people only. By subtracting our 80 from the total amount of people who have been counted with this trait we get

140-80= 60

So there are a total of 60 people in region II that have dark hair that is not short

Region III- We use the same logic in this area to determine how many short haired people there are that do not also have dark hair

90-80=10

There are 10 people in region IIII with short hair that is not dark

Region IV- this variable is given in the question, so the number of people here who have neither short nor dark hair is 50

We can add the total up to make sure it checks out

80+60+10+50=200

confidence rating #$&*:

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Self-critique Rating:

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Self-critique (if necessary):

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Self-critique rating:

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Very good. Good self-critiques, especially.

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Note that you need to fill in your access code. At the very beginning of the term, until I'm sure everyone has their codes, I fill them in. However we're past that point, or will be very soon.

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Good. You caught it yourself, as I see with your second submission.

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