<PRE><B>Question 820418</B>
Suppose we want a 90% confidence interval for the average amount spent on books by freshman in their first year at college. The amount spent has a normal distribution with standard deviation $20. 
(a) How large should the sample be if the margin of error is 
to be less than $2?
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Since E = z*s/sqrt(n)
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n = [z*s/E]^2
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n = [1.645*20/2]^2 = 16.45^2 = 271 when rounded up
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Cheers,
Stan H.
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