Posted by **Robin** on Sunday, September 5, 2010 at 4:44pm.

A group of statistics students decided to conduct a survey at their university to find the average (mean) amount of time students spent studying per week. Assuming a standard deviation of 3 hours, what is the required sample size if the error should be less than ½ hour with a 99% level of confidence?

- Statistics -
**MathGuru**, Monday, September 6, 2010 at 7:04pm
Formula:

n = [(z-value * sd)/E]^2

...where n = sample size, z-value will be 2.58 using a z-table to represent the 99% confidence interval, sd = 3, E = 0.5, ^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 -
**me**, Friday, December 3, 2010 at 1:20am
Using a Z-value of 2.575, the answer is 238.7; or 240 if the answer is in multiple choice form.

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