Venn diagram problem (either)

In summary, the answer to the question "How many students take either reading or sports?" depends on the interpretation of the phrase "either reading or sports." If it is interpreted as the exclusive or, meaning the students like one or the other but not both, then the answer is 55. However, if it is interpreted as the inclusive or, meaning the students like at least one of the two activities, then the answer is 70. The interpretation may depend on the context and wording of the question.
  • #1
tzx9633

Homework Statement


In a school . 35 students like reading , 50 student like jogging , and 15 students like both . How many person like either reading or sports ?

The ans is 35+ 50 -15 = 70 ( Ans given)

but , i think the ans should be 20+ 35 = 55 only

Which is correct ? If my ans is wrong , in what circumstances , the ans would be 20+ 35 = 55 ??

Homework Equations

The Attempt at a Solution

 

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  • #2
I agree with your Venn diagram, and I guess it just boils down to how we interpret "like either reading or sports." It we take that to mean likes one or the other, but not both, then it is 55, but if we take it to mean likes at least one of the two, then it is 70. :biggrin:
 
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  • #3
MarkFL said:
I agree with your Venn diagram, and I guess it just boils down to how we interpret "like either reading or sports." It we take that to mean likes one or the other, but not both, then it is 55, but if we take it to mean likes at least one of the two, then it is 70. :biggrin:
The "either reading or sports" should be interpreted as the exclusive or, not the inclusive or. IOW, the ones who like reading don't like sports, and the ones who like sports don't like reading. Without the word "either" it would be reasonable to assume that some like both activities.
 
  • #4
Mark44 said:
The "either reading or sports" should be interpreted as the exclusive or, not the inclusive or. IOW, the ones who like reading don't like sports, and the ones who like sports don't like reading. Without the word "either" it would be reasonable to assume that some like both activities.

I agree, and that's how I would interpret it as well, just as the OP did. :smile:
 
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  • #5
tzx9633 said:

Homework Statement


In a school . 35 students like reading , 50 student like jogging , and 15 students like both . How many person like either reading or sports ?

The ans is 35+ 50 -15 = 70 ( Ans given)

but , i think the ans should be 20+ 35 = 55 only

Which is correct ? If my ans is wrong , in what circumstances , the ans would be 20+ 35 = 55 ??

Homework Equations

The Attempt at a Solution

In Logic and in Probability the word "or" (almost always) means "inclusive or", so "A or B" normally means "A or B or both". In set language this would be ##A \cup B##, while "A or B but not both" would be ##(A-B) \cup (B-A) = A \cup B - A \cap B##.

However, to be honest, it becomes a bit trickier when the word "either" is inserted, as it is in your case; then I think the situation is less settled. I have seen it interpreted in different ways in different sources.
 
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  • #6
Ray Vickson said:
"A or B" normally means "A or B or both"
Thanks for the point !
 
  • #7
Ray Vickson said:
However, to be honest, it becomes a bit trickier when the word "either" is inserted, as it is in your case; then I think the situation is less settled. I have seen it interpreted in different ways in different sources.
I agree with what you said regarding "A or B," but most of the cases I've seen with "either A or B," the intended meaning is one of the two alternatives, but not both. I can't cite any authoritative mathematical sources for this, but the Merriam-Webster dictionary defines "either-or" as "an unavoidable choice or exclusive division between only two alternatives".

Side note: Thread moved to the Precalc section.
 
  • #8
Mark44 said:
I agree with what you said regarding "A or B," but most of the cases I've seen with "either A or B," the intended meaning is one of the two alternatives, but not both. I can't cite any authoritative mathematical sources for this, but the Merriam-Webster dictionary defines "either-or" as "an unavoidable choice or exclusive division between only two alternatives".

Side note: Thread moved to the Precalc section.

Your citation of "an unavoidable choice or exclusive division between only two alternatives" should be very helpful to the OP, because he/she needs to ask: is every student forced to like either jogging or reading but never both? That would be an unavoidable choice between two alternatives. Furthermore, when WE count the cases we are not performing any choice at all, we are just sorting the data, so we probably are not performing an unavoidable choice either.

I looked further into this on-line, by Googling "either-or in probability"; just about every web page (some including the word "either" and some not) use the inclusive-or form.

So, for the OP: the bottom line is that your book agrees with most others on the subject. That is the reason for the computation it performed.

Perhaps a more extreme example may help. Suppose that in a particular group of 100 students, 90 take physics, 90 take chemistry and 85 take both. How many students take either physics or chemistry? One (purely arithmetical) answer is 90 + 90 = 180, but this goes against the "spirit" of the question. A more complete statement of the question might be "In this group of 100 students, how many take either physics or chemistry?" My previous version of the question just left out the part in red, but I think most people would agree that it is probably implicit.
 
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1. What is a Venn diagram?

A Venn diagram is a visual representation of mathematical or logical relationships between different sets of objects. It consists of overlapping circles or other shapes that represent the sets, and the overlapping regions indicate the shared elements between the sets.

2. How do you read a Venn diagram?

To read a Venn diagram, start by identifying the sets represented by each circle or shape. Then, look at the overlapping regions to determine the shared elements between the sets. The elements outside of the circles or shapes represent elements that are not included in either set.

3. How do you solve a Venn diagram problem?

To solve a Venn diagram problem, first identify the sets involved and the information given about each set. Then, use this information to fill in the appropriate regions of the diagram. Finally, use the diagram to answer the specific question being asked.

4. What is the purpose of using a Venn diagram?

Venn diagrams are useful for visually organizing and understanding relationships between different sets of data or information. They can also be used to identify similarities and differences between sets, and to solve mathematical or logical problems.

5. Can a Venn diagram have more than three sets?

Yes, a Venn diagram can have more than three sets. However, as the number of sets increases, the diagram can become more complex and difficult to read. In these cases, it may be helpful to use other types of visual aids, such as tables or charts, to represent the relationships between the sets.

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