Posted by Sarah on Monday, September 13, 2010 at 7:58pm.
Scores on a certain test are normally distributed with a variance of 14. A researcher wishes to estimate the mean score achieved by all adults on the test. Find the sample size needed to assure with 95% confidence that the sample mean will not differ from the population mean by more than 2 units

statistics  MathGuru, Monday, September 13, 2010 at 8:11pm
Formula:
n = [(zvalue * sd)/E]^2
...where n = sample size, zvalue will be 1.96 using a ztable to represent the 95% confidence interval, sd = square root of 14 (standard deviation is equal to the square root of the variance), E = 2, ^2 means squared, and * means to multiply.
Plug the values into the formula and finish the calculation. Round your answer to the next highest whole number.

statistics  Sarah, Monday, September 13, 2010 at 8:24pm
So the answer would be 13.4459 ?

statistics  MathGuru, Monday, September 13, 2010 at 9:23pm
Looks OK! Round up to the next highest whole number, which would be 14.

statistics  Edddddy, Monday, February 28, 2011 at 1:56am
Thanks MathGuru, the formula helped with a relevant math problem.
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