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Math Help - Help figuring out Probabilities:

  1. #1
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    Help figuring out Probabilities:

    For df=25, determine the value of A that corresponds to each of the following probabilities:

    a) P(t ≥A) =0.025
    b) P(t ≤ A) =0.10
    c) P (-A ≤ t ≤ A) =0.99
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  2. #2
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    Quote Originally Posted by loriemomof2 View Post
    For df=25, determine the value of A that corresponds to each of the following probabilities:

    a) P(t ≥A) =0.025
    b) P(t ≤ A) =0.10
    c) P (-A ≤ t ≤ A) =0.99
    What distribution does A follow?
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  3. #3
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    Smile

    I am not sure that I am understanding your question, as the problem I entered is as it is listed in my book, however my instructor explained it as this:

    For df=25, determine the value of A that corresponds to each of the following probabilities:

    a) P(t ≥A) =0.025
    b) P(t ≤ A) =0.10
    c) P (-A ≤ t ≤ A) =0.99



    The
    a) A = 2.060
    b) P(t ≤ A) =0.10 implies P(t >= A) = 0.90
    Thus, A = -1.316
    c) Since t-distribution is symmetric, P (-A ≤ t ≤ A) =0.99 implies that we need to find A such that P(t >= A) = (1-0.99)/2=0.005
    Thus, A = 2.787
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  4. #4
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    Quote Originally Posted by loriemomof2 View Post
    I am not sure that I am understanding your question, as the problem I entered is as it is listed in my book, however my instructor explained it as this:

    For df=25, determine the value of A that corresponds to each of the following probabilities:

    a) P(t ≥A) =0.025
    b) P(t ≤ A) =0.10
    c) P (-A ≤ t ≤ A) =0.99


    The
    a) A = 2.060
    b) P(t ≤ A) =0.10 implies P(t >= A) = 0.90
    Thus, A = -1.316
    c) Since t-distribution is symmetric, P (-A ≤ t ≤ A) =0.99 implies that we need to find A such that P(t >= A) = (1-0.99)/2=0.005
    Thus, A = 2.787
    I assume that the red part of part c) contains the answer to the question that I asked ....

    Are you expected to use the pdf or use technology ....? It's hard to give help if the tools that you're required to use are not known ....
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  5. #5
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    Cool

    Quote Originally Posted by mr fantastic View Post
    I assume that the red part of part c) contains the answer to the question that I asked ....

    Are you expected to use the pdf or use technology ....? It's hard to give help if the tools that you're required to use are not known ....
    Can you imagine how we feel as non math geniusesí if those of you who understand this stuff can not figure it out?

    As all we know is that we are to figure out what to do with the problem, yet to us it looks as though it is written in a foreign language.
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  6. #6
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    Quote Originally Posted by loriemomof2 View Post
    Can you imagine how we feel as non math geniusesí if those of you who understand this stuff can not figure it out?

    As all we know is that we are to figure out what to do with the problem, yet to us it looks as though it is written in a foreign language.
    How can I help you if you don't say what tools you've been given to answer questions like this. There are several ways of answering it.

    Perhaps you're expected to use a table of critical values like the one found here: 1.3.6.7.2. Upper Critical Values of the Student's-t Distribution

    In which case it is clear that the answers are:

    a) 2.060
    b) and c) Your instructor has already outlined how to do it. The numbers your instructor used are got from tables like in the one in the above hyperlink.

    If you cooperated by answering the questions I asked it would have been easier to help you.

    By the way, the reason I asked what distribution A followed is that many distributions are characterised by degree of freedom. Without knowing which one in particular it was impossible to help you without having to make a guess which one .... Why guess, I thought, when I can simply ask for clarification ....... The fact that you could not tell me suggests you have deeper problems than the one you posted - you're advised to get as much help as possible from your instructor.

    Furthermore, even when the distribution is known, their are several ways of answering the question. Numerical integration of the pdf, black-box technology, tables of critical values etc. Again, why guess, I thought, when I can simply ask for clarification .......
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