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Posted by on Tuesday, December 6, 2011 at 3:48pm.

Find a confidence interval for ƒÊ assuming that each sample is from a normal population.
a. P x = 14, ƒÐ = 4, n = 5, 90 percent confidence
b. P x = 37, ƒÐ = 5, n = 15, 99 percent confidence
c. P x = 121, ƒÐ = 15, n = 25, 95 percent confidence

Need to show my work/formula
Thanks,

  • Math-Statistics - , Tuesday, December 6, 2011 at 4:58pm

    Assuming two-tailed test, x = mean, ƒD = Standard deviation:

    90% = mean ± 1.645 SEm

    SEm = SD/√n = Standard Error of the mean

    99% = mean ± 2.575 SEm

    95% = mean ± 1.96 SEm

    Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportions and their related Z scores.

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