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    Hi! I'm really stuck on this question and wondered if anybody could help explain it to me?
    Thanks!Attachment 699798
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    (Original post by ProbablyJade)
    Hi! I'm really stuck on this question and wondered if anybody could help explain it to me?
    Thanks!Attachment 699798
    It's a very iffy question you've been given, IMO.

    To start, what quartiles do the 850 and 1100 marks represent?

    And so what's the fraction of the whole that this represents?

    Hence the probabilty of a single person chosen at random being between those bounds is...?

    Can you finish from there.
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    (Original post by ghostwalker)
    It's a very iffy question you've been given, IMO.

    To start, what quartiles do the 850 and 1100 marks represent?

    And so what's the fraction of the whole that this represents?

    Hence the probabilty of a single person chosen at random being between those bounds is...?

    Can you finish from there.
    So, when i attempted the question i thought that the 850 was the 50% quartile and the 1000 was the 75% quartile. Therefore the question is asking me to find the probability that the 3 members were between the average and 25% above the average. I thought that the probability of a single person being in those bounds was 7.5/30 as 25% of 30 is 7.5...
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    (Original post by ProbablyJade)
    So, when i attempted the question i thought that the 850 was the 50% quartile and the 1000 was the 75% quartile. Therefore the question is asking me to find the probability that the 3 members were between the average and 25% above the average. I thought that the probability of a single person being in those bounds was 7.5/30 as 25% of 30 is 7.5...
    Agreed, p=0.25, or as a fraction 1/4.

    We're going to have to assume that the three are chosen with replacement, otherwise the choices won't be independent. Question's wording seems to imply otherwise, though it doesn't explicitly state that, and that would give none of those answers.

    So, the probability of each chosen one being in the desired range is 1/4.

    And since they're independent probabilty of all three being in the range is (1/4)^3
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    (Original post by ghostwalker)
    Agreed, p=0.25, or as a fraction 1/4.

    We're going to have to assume that the three are chosen with replacement, otherwise the choices won't be independent. Question's wording seems to imply otherwise, though it doesn't explicitly state that, and that would give none of those answers.

    So, the probability of each chosen one being in the desired range is 1/4.

    And since they're independent probabilty of all three being in the range is (1/4)^3
    I checked and that is the right answer. I went wrong because i assumed that it was without replacement and did 7.5/30 * 6.5/29 * 5.5/28
    Thanks for your help!
 
 
 
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