Question 808112
You are 
planning to select n batteries of this type and to 
operate them continuously until they fail. You 
have some feeling that the standard deviation of 
the lifetimes should be around 20 hours, and you 
wish your estimate of µ to be within 1 hour of 
µ with 95% confidence. How many batteries 
should you select? 
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n = [z*s/E]^2
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n =[1.96*20/1]^2 = 39.2^2 = 1567 when rounded up
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Cheers,
Stan H.
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