statistics

Assume that a standardized test is designed to have the mean score of 100 and the standard deviation of 15. At the 95% confidence interval, how large does the sample size have to be if the margin of error is to be 3 points?

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1. Formula:

n = {[(z-value) * sd]/E}^2
...where n = sample size, sd = standard deviation, E = maximum error, and ^2 means squared.

Using the values you have in your problem:

n = {[(1.96) * 15]/3}^2

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