## Question 903:

Consider a random sample of 9 observations, from a Normal distribution, with sample average 25.0.a) Calculate a 95% confidence interval for the population mean μ when the standard deviation (σ) is known to be equal to 3.0.

b) Repeat a) when instead the standard deviation is unknown and is estimated as s = 3.0.

c) Explain the difference, if any, in width between these two intervals.