Current Attempt in Progress The standard deviation for a population is = 14.3. A sample of 19 observations selected from this population gave a mean equal to 138.80. The population is known to have a normal distribution. Round your answers to two decimal places. a. Make a 98% confidence interval for . b. Construct a 95% confidence interval for . c. Determine a 90% confidence interval for . d. Does the width of the confidence intervals constructed in parts a through c decrease as the confidence level decreases