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

Find a confidence interval for assuming that each sample is from a normal population.

a. P x = 14, = 4, n = 5, 90 percent confidence

b. P x = 37, = 5, n = 15, 99 percent confidence

c. P x = 121, = 15, n = 25, 95 percent confidence

Need to show my work/formula

Thanks,

- Math-Statistics -
**PsyDAG**, Tuesday, December 6, 2011 at 4:58pm
Assuming two-tailed test, x = mean, D = 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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