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2. Suppose that we have a population which distribution is approximately normal and the standard deviation is known (but not given here). Suppose we obtained (65,77) for the 90% condence interval for the population mean, using the formula :73 :: Za/z- This condence interval is based on a simple random sample of 25 observations. Calculate (a) the sample mean :73. (b) the margin of error (e) the population standard deviation 0 Now instead suppose that population standard deviation is unknown and therefore is estimated by the sample standard deviation 3. Further suppose the sample size is n = 9. Assuming that the tbased 90% condence interval for a population mean is still (65, 77), calculate the (d) the sample mean :73 (e) the margin of error (f) the sample standard deviation 3