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I need to figure out the Probability that $Y > 23$ for a chi-square distribution with degrees of freedom $= 7$.

The book says to do this with some applet. I don't know what it's talking about.

Can I do this on my Ti-89 (preferable) or on some website somewhere?

EDIT/UPDATE:

I found a program on my ti-89 for chi-square distribution. However it asks me for lower and upper bound and degrees of freedom. I put in $7$ for degrees of freedom but i'm not sure how to translate probability $Y > 23$ into an upper and lower bound?

I put in lower $= 0$, upper $= 23$, degrees of freedom $= 7$ and I said to auto-scale and I got $.998295$. Is that the right probability?

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    [This](http://education.ti.com/calculators/downloads/US/Software/Detail?id=189) could have just been found using a search engine. Voting to close.2010-11-02
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    I'm confused as to how this answers my question. I don't see anywhere that it says this program can preform the calculation I need.2010-11-02
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    And I did google my question. This did not come up.2010-11-02
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    and i believe I have this on my calculator already because I can get to the screen that is shown, and I cannot figure out how to use it to solve my problem.2010-11-02
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    But you did read that app's manual, yes?2010-11-02
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    nope. I didn't see it. Thought that was a link to download the program. I found the program and am reading the manual but still don't get how to use the program. I'll edit my question.2010-11-03
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    A hint: on these calculators, $-10^{99}$ and $10^{99}$ are stand-ins for $-\infty$ and $\infty$.2010-11-03
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    Ive seen the calculator give me artifacts a bunch of times, they always have more 99s than this did. If it was tyring to give me an artifact meaning 1 it would have said .9999998 or 1.000001 . I'm thinking that .998295 is the actual value. is there a table with these numbers in them?2010-11-03
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    The expected value of the chi-square is 7, so $Y > 23$ is an improbable event. You probably want $1-.998295 = .001705$.2010-11-03

1 Answers 1

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There's an online calculator here. Plugging $\chi^2 = 23$ and $df=7$, we get $.0017$. Your calculator calculated the probability that $0 \leq \chi^2 \leq 23$, which is $1-.0017 = .9983$.

As I commented above, you could tell that you needed to take $1-p$ instead of $p$ since $\chi^2 > 23$ is an unlikely event, given that the expectation is $7$ and the standard deviation is $\sqrt{14} \approx 4$ (Chebyshev and even Markov would give you that $p < 1/2$).

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    Good think you need more than just one vote to close or I would never have gotten this excellent answer. Thanks!2010-11-03