basic math question Forum
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basic math question
If top 15% gets A for Class 1
If top 15% gets A for Class 2
Then if student gets two A's, what % of the class is he in - for sure?
Is it 7.5% or something like that? Sorry, I majored in history and I'm not sure how this works.
If top 15% gets A for Class 2
Then if student gets two A's, what % of the class is he in - for sure?
Is it 7.5% or something like that? Sorry, I majored in history and I'm not sure how this works.
- Mrs. Jack Donaghy
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Re: basic math question
is said student only taking those two classes?
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Re: basic math question
I'm trying to answer this question for 4 law school classes, of course, but I'm reducing n to 2 so I can get an answer to the question.
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Re: basic math question
Top 15% is the only "for sure" answer, I think. The person could be the top-ranked kid in the two classes if no other student got both A's, so he could be top 1% or whatever, but the worst he could be is top 15%
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- Mrs. Jack Donaghy
- Posts: 57
- Joined: Fri Apr 09, 2010 2:15 am
Re: basic math question
titcr.handlebutton wrote:Top 15% is the only "for sure" answer, I think. The person could be the top-ranked kid in the two classes if no other student got both A's, so he could be top 1% or whatever, but the worst he could be is top 15%
- thesealocust
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Re: basic math question
edited / never mind
Last edited by thesealocust on Mon Jun 28, 2010 8:11 pm, edited 1 time in total.
- johnstuartmill
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Re: basic math question
The answer for four classes is also 15% (assuming that the 'A' cutoff in those classes the same). After all, you can't rule out the possibility that everyone who gets an A in one class also gets one in all the others, right? But that's pretty unlikely -- four A's would probably put a person much higher than that. We just can't say anything with any certainty except for that 15%.handlebutton wrote:I'm trying to answer this question for 4 law school classes, of course, but I'm reducing n to 2 so I can get an answer to the question.
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Re: basic math question
Top 15% is the only thing we can say with complete certainty, but it is not a likely scenario. The probability is much greater that student would be higher; I am too far removed from my last math class to do any adequate analysis on what the percentile with the highest probability would be.johnstuartmill wrote:The answer for four classes is also 15% (assuming that the 'A' cutoff in those classes the same). After all, you can't rule out the possibility that everyone who gets an A in one class also gets one in all the others, right? But that's pretty unlikely -- four A's would probably put a person much higher than that. We just can't say anything with any certainty except for that 15%.handlebutton wrote:I'm trying to answer this question for 4 law school classes, of course, but I'm reducing n to 2 so I can get an answer to the question.
- johnstuartmill
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- Joined: Fri May 22, 2009 9:53 pm
Re: basic math question
There's no way to answer that question without more data than is in the OP.tomwelling wrote:Top 15% is the only thing we can say with complete certainty, but it is not a likely scenario. The probability is much greater that student would be higher; I am too far removed from my last math class to do any adequate analysis on what the percentile with the highest probability would be.johnstuartmill wrote:The answer for four classes is also 15% (assuming that the 'A' cutoff in those classes the same). After all, you can't rule out the possibility that everyone who gets an A in one class also gets one in all the others, right? But that's pretty unlikely -- four A's would probably put a person much higher than that. We just can't say anything with any certainty except for that 15%.handlebutton wrote:I'm trying to answer this question for 4 law school classes, of course, but I'm reducing n to 2 so I can get an answer to the question.
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Re: basic math question
If law students' grades in every class were completely independent (0 correlation), you would expect about 15% of 15%, or 2.25% (if my mental math doesn't suck) of students to have A's in both classes in the example given. However, grades are almost certainly not independent; some students tend to do well in a number of classes and some students tend to do poorly in most. As everyone else has said, it's always possible that all 15% from the first class get A's in the second and so you can never be sure that you're doing any better than 15% (correlation of 1). Without more information, there's really no way to know where you fall in between those two numbers (there is always the possibility that there is a negative correlation, and so fewer than 2.25% would have A's in both classes, but this seems quite unlikely).
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