Problem 10-9 A sample of 40 observations is taken from a population of unknown mean wherein the standard deviation is assumed to be 5 grams. The computed value of the sample mean is 38.0 grams. Construct confidence intervals for each of the following levels of confidence: (a) 90% Confidence Interval

(36.7, 39.3)

Step-by-step explanation:

Confidence interval for population mean:

, where n= sample size, = sample mean, = population standard deviation, = critical z value.

Given: n= 40 ,

Critical z-value for 90% confidence = 1.645

Then, required confidence interval:

Hence, a 90% Confidence Interval =  (36.7, 39.3)