Chebyshevs theorem : find k so that at most 10%

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Discussion Overview

The discussion revolves around Chebyshev's theorem and the interpretation of the parameter k in relation to a statistics problem involving test scores. Participants explore how to determine k such that at most 10% of the scores are more than k standard deviations above the mean, considering the unknown distribution of scores.

Discussion Character

  • Debate/contested
  • Mathematical reasoning
  • Homework-related

Main Points Raised

  • One participant suggests that k could be calculated using the equation 1 - 1/k^2 = 0.1, leading to k = 1.05, but expresses confusion over the correct interpretation of the question.
  • Another participant proposes that the minimal value for k, given "at most" 10%, should be derived from 1 - 1/k^2 = 0.8, resulting in k = 2.236, assuming a symmetrical distribution.
  • Some participants question the interpretation of "at most" 10%, arguing that it implies anything not greater than 10%, and discuss the implications of this phrasing on the calculation of k.
  • Further clarification is provided that if k is set at 2.236, then 10% of scores would be at least 2.236 SD above the mean, and any value of k greater than 2.236 would also satisfy the condition.
  • A participant confirms their understanding that the value of k should account for the last 10% of scores on either side of the mean, leading to the conclusion that 80% of scores lie within 2.236 SD of the mean.

Areas of Agreement / Disagreement

Participants express differing interpretations of the question and the implications of "at most" 10%. While some agree on the calculation of k as 2.236, others challenge the reasoning and the assumptions made regarding the distribution.

Contextual Notes

The discussion reflects varying assumptions about the distribution of scores and the interpretation of statistical terms, which may affect the conclusions drawn by participants.

idioteque
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the test scores for a large statistics class have an unknown distribution with a mean of 70 and a standard deviation of 10

find k so that at most 10% of the scores are more than k standard deviations above the mean.

I'm a bit confused by the question it self.
does the question means :
1-1/k^2 = 0.1
k = 1.05

or

1-1/k^2 = 0.2
k = 1.12

or

1-1/k^2 = 0.8
k = square root 5 = 2.23

pls help, thanks in advance.
 
Last edited:
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to avoid being flamed for homework type of question, I added my own opinion towards this question. your help is very much appreciated.
 
idioteque said:
to avoid being flamed for homework type of question, I added my own opinion towards this question. your help is very much appreciated.

I misread your question. The minimal value for k given "at most" 10% k SDs above the mean would be [tex]1-1/k^2=0.8[/tex] so [tex]k=2.236[/tex]. This assumes your distribution is perfectly symmetrical.
 
Last edited:
'at most' 10%.

why take the other remaining 80%?
it asked for 'at most' 10%.
doesn't this mean anything not greater than 10%?
if it asked 'at least' 10% then anything greater than 10%
 
idioteque said:
'at most' 10%.

why take the other remaining 80%?m
it asked for 'at most' 10%.
doesn't this mean anything not greater than 10%?
if it asked 'at least' 10% then anything greater than 10%

80% of the test scores are within 2.236 SD of the mean. 10% are at least 2.236 SD above the mean, 10% at least 2.236 SD below the mean. This is the minimal value of k. If you want to be sure that at most 10% are more than k SD above the mean, take any arbitrary value of k greater than 2.236. That's the way I read it anyway.
 
Last edited:
ok thank you. I got it.
the keyword is above the mean.
the value of k before the last 10% of each side(20%). so 80% is in between the 20%
is how I interpreted it as it is.
correct?
 
idioteque said:
s how I interpreted it as it is.
correct?

Correct.
 

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