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?

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  1. 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.

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  2. 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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