Posted by **Valerie** on Tuesday, November 2, 2010 at 9:02pm.

A researcher is interested in estimating the noise levels in decibels at area urban hospitals. She wants to be 90% confident that her estimate is correct. If the standard deviation is 4.13, how large a sample is needed to get the desired information to be accurate within 0.68 decibels?

- statistics -
**MathGuru**, Friday, November 5, 2010 at 7:42pm
Formula:

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

...where n = sample size, z-value will be found using a z-table for 90% confidence, sd = 4.13, E = 0.68, ^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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