<PRE><B>Question 296296</B>
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 4.8, how large a sample is needed to get the desired information to be accurate within 0.60 decibels? 
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Since E = zs/sqrt(n)
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Formula n = [z*s/E]^2
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n = [1.645*4.8/0.6]^2
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n = 173 when rounded down.
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Cheers,
Stan H.</PRE>