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Question

The result of a fitness trial is a random variable X which is normally distributed with mean µ and standard deviation 2.4 . A researcher uses the results from a random sample of 90 trials to calculate a 98% confidence interval for µ . What is the width of this interval?

Answer 1

Since this is a normal distribution, the confidence interval is calculated as: CI= (µ - z* σ/√n, µ + z* σ/√n), where µ is sample mean, σ standard deviation and z is critical value associated with confidence level (z=2.326 for 98% confidence level). In this case we simply calculate the width as: 2.326* 2.4/√90 = 0.589.