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Choose a sample size from an exact normal mean distribution
The life, in hours, of a randomly chosen light bulb is normally distributed with mean 1100 and standard deviation 70. How large a sample is required so that the probability that its mean life exceeds 1120 is not more than 5%? Do you need the central limit theorem?
CJC · Discussion · Question 6
Normality of the population already supplies the distribution of its sample mean.