<PRE><B>Question 462607</B>
A study of one-millimeter crystal marbles used in making crystal chandeliers showed that the standard deviation of the weight a crystal marble is 250 milligrams. 
A crystal chandelier manufacturer wishes to find the 90% confidence interval for the average weight of a one-millimeter crystal marble. 
How many crystal marbles does she need to weigh to be accurate within 15 milligrams
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n = [z*s/E]^2
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n = [1.645*250/15]^2 = 752 when rounded up
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Cheers,
Stan H.
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