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Artusartos
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Let [itex]\bar{X}[/itex] be the mean of a random sample of size n from a distribution that is [itex]N(\mu,9)[/itex]. Find n such that [itex]P(\bar{X}-1 < \mu < \bar{X}+1)=.90[/itex], approximately.
My answer:
[tex]-Z^* < \frac{\bar{X}-\mu}{9/\sqrt(n)} < Z^* [/tex] where [itex]-Z^*[/itex] and [itex]Z^*[/itex] are the critical values.
So...
For the confidence interval, we have [tex]\bar{x} \pm z^*(\frac{9}{\sqrt(n)})[/tex]
When I looked up the normal table for [itex]z^*[/itex], I found that it was approximately equal to 1.29Since the question tells us that the confidence interval is [tex]\bar{X} \pm 1 [/tex], so I just solved [tex]1 = (1.29)(\frac{9}{\sqrt(n)})[/tex]...but my answer was wrong...it was supposed to be 24 or 25. Can anybody please help?
Thanks in advance
My answer:
[tex]-Z^* < \frac{\bar{X}-\mu}{9/\sqrt(n)} < Z^* [/tex] where [itex]-Z^*[/itex] and [itex]Z^*[/itex] are the critical values.
So...
For the confidence interval, we have [tex]\bar{x} \pm z^*(\frac{9}{\sqrt(n)})[/tex]
When I looked up the normal table for [itex]z^*[/itex], I found that it was approximately equal to 1.29Since the question tells us that the confidence interval is [tex]\bar{X} \pm 1 [/tex], so I just solved [tex]1 = (1.29)(\frac{9}{\sqrt(n)})[/tex]...but my answer was wrong...it was supposed to be 24 or 25. Can anybody please help?
Thanks in advance
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